[ruby/json] Encoding benchmark updates

Remove `rapidjson` as it's 2x slower most benchmarks, and on
par on a couple of them, so it's not telling us much here.

Configure `Oj` in compat mode so it generate the same JSON
on the `many to_json` benchmark.

```
== Encoding small nested array (121 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
        json (reuse)   220.202k i/100ms
                json   162.190k i/100ms
                  oj   222.094k i/100ms
Calculating -------------------------------------
        json (reuse)      2.322M (± 1.3%) i/s  (430.72 ns/i) -     11.671M in   5.027655s
                json      1.707M (± 1.2%) i/s  (585.76 ns/i) -      8.596M in   5.035996s
                  oj      2.248M (± 1.4%) i/s  (444.94 ns/i) -     11.327M in   5.040712s

Comparison:
        json (reuse):  2321686.9 i/s
                  oj:  2247509.6 i/s - 1.03x  slower
                json:  1707179.3 i/s - 1.36x  slower

== Encoding small hash (65 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
        json (reuse)   446.184k i/100ms
                json   265.594k i/100ms
                  oj   653.226k i/100ms
Calculating -------------------------------------
        json (reuse)      4.980M (± 1.4%) i/s  (200.82 ns/i) -     24.986M in   5.018729s
                json      2.763M (± 1.8%) i/s  (361.94 ns/i) -     13.811M in   5.000434s
                  oj      7.232M (± 1.4%) i/s  (138.28 ns/i) -     36.581M in   5.059377s

Comparison:
        json (reuse):  4979642.4 i/s
                  oj:  7231624.4 i/s - 1.45x  faster
                json:  2762890.1 i/s - 1.80x  slower

== Encoding mixed utf8 (5003001 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json    34.000 i/100ms
                  oj    36.000 i/100ms
Calculating -------------------------------------
                json    357.772 (± 4.8%) i/s    (2.80 ms/i) -      1.802k in   5.047308s
                  oj    327.521 (± 1.5%) i/s    (3.05 ms/i) -      1.656k in   5.057241s

Comparison:
                json:      357.8 i/s
                  oj:      327.5 i/s - 1.09x  slower

== Encoding mostly utf8 (5001001 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json    26.000 i/100ms
                  oj    36.000 i/100ms
Calculating -------------------------------------
                json    294.357 (±10.5%) i/s    (3.40 ms/i) -      1.456k in   5.028862s
                  oj    352.826 (± 8.2%) i/s    (2.83 ms/i) -      1.764k in   5.045651s

Comparison:
                json:      294.4 i/s
                  oj:      352.8 i/s - same-ish: difference falls within error

== Encoding twitter.json (466906 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json   206.000 i/100ms
                  oj   229.000 i/100ms
Calculating -------------------------------------
                json      2.064k (± 9.3%) i/s  (484.55 μs/i) -     10.300k in   5.056409s
                  oj      2.121k (± 8.4%) i/s  (471.47 μs/i) -     10.534k in   5.012315s

Comparison:
                json:     2063.8 i/s
                  oj:     2121.0 i/s - same-ish: difference falls within error

== Encoding citm_catalog.json (500298 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json   119.000 i/100ms
                  oj   126.000 i/100ms
Calculating -------------------------------------
                json      1.317k (± 2.3%) i/s  (759.18 μs/i) -      6.664k in   5.061781s
                  oj      1.261k (± 2.9%) i/s  (793.11 μs/i) -      6.300k in   5.000714s

Comparison:
                json:     1317.2 i/s
                  oj:     1260.9 i/s - same-ish: difference falls within error

== Encoding canada.json (2090234 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json     1.000 i/100ms
                  oj     1.000 i/100ms
Calculating -------------------------------------
                json     19.590 (± 0.0%) i/s   (51.05 ms/i) -     98.000 in   5.004485s
                  oj     19.003 (± 0.0%) i/s   (52.62 ms/i) -     95.000 in   5.002276s

Comparison:
                json:       19.6 i/s
                  oj:       19.0 i/s - 1.03x  slower

== Encoding many #to_json calls (2701 bytes)
ruby 3.4.0preview2 (2024-10-07 master https://github.com/ruby/json/commit/32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json     2.556k i/100ms
                  oj     2.332k i/100ms
Calculating -------------------------------------
                json     25.367k (± 1.7%) i/s   (39.42 μs/i) -    127.800k in   5.039438s
                  oj     23.743k (± 1.5%) i/s   (42.12 μs/i) -    118.932k in   5.010303s

Comparison:
                json:    25367.3 i/s
                  oj:    23743.3 i/s - 1.07x  slower

```

https://github.com/ruby/json/commit/5a64fd5b6f

1 files changed, 11 insertions, 6 deletions

diff --git a/benchmark/encoder.rb b/benchmark/encoder.rb
index 2b02d5d5e9..662b1c3e7f 100644
--- a/benchmark/encoder.rb
+++ b/benchmark/encoder.rb
@@ -1,7 +1,8 @@
 require "benchmark/ips"
 require "json"
 require "oj"
-require "rapidjson"
+
+Oj.default_options = Oj.default_options.merge(mode: :compat)
 
 if ENV["ONLY"]
   RUN = ENV["ONLY"].split(/[,: ]/).map{|x| [x.to_sym, true] }.to_h
@@ -15,12 +16,10 @@ end
 
 def implementations(ruby_obj)
   state = JSON::State.new(JSON.dump_default_options)
-
   {
     json_state: ["json (reuse)", proc { state.generate(ruby_obj) }],
     json: ["json", proc { JSON.dump(ruby_obj) }],
     oj: ["oj", proc { Oj.dump(ruby_obj) }],
-    rapidjson: ["rapidjson", proc { RapidJSON.dump(ruby_obj) }],
   }
 end
 
@@ -38,6 +37,11 @@ def benchmark_encoding(benchmark_name, ruby_obj, check_expected: true, except: [
         result = block.call
         if check_expected && expected != result
           puts "#{name} does not match expected output. Skipping"
+          puts "Expected:" + '-' * 40
+          puts expected
+          puts "Actual:" + '-' * 40
+          puts result
+          puts '-' * 40
           next
         end
       rescue => error
@@ -67,12 +71,13 @@ benchmark_encoding "citm_catalog.json", JSON.load_file("#{__dir__}/data/citm_cat
 
 # This benchmark spent the overwhelming majority of its time in `ruby_dtoa`. We rely on Ruby's implementation
 # which uses a relatively old version of dtoa.c from David M. Gay.
-# Oj is noticeably faster here because it limits the precision of floats, breaking roundtriping. That's not
-# something we should emulate.
+# Oj in `compat` mode is ~10% slower than `json`, but in its default mode is noticeably faster here because
+# it limits the precision of floats, breaking roundtriping.  That's not something we should emulate.
+#
 # Since a few years there are now much faster float to string implementations such as Ryu, Dragonbox, etc,
 # but all these are implemented in C++11 or newer, making it hard if not impossible to include them.
 # Short of a pure C99 implementation of these newer algorithms, there isn't much that can be done to match
 # Oj speed without losing precision.
 benchmark_encoding "canada.json", JSON.load_file("#{__dir__}/data/canada.json"), check_expected: false, except: %i(json_state)
 
-benchmark_encoding "many #to_json calls", [{Object.new => Object.new, 12 => 54.3, Integer => Float, Time.now => Date.today}] * 20, except: %i(json_state)
+benchmark_encoding "many #to_json calls", [{object: Object.new, int: 12, float: 54.3, class: Float, time: Time.now, date: Date.today}] * 20, except: %i(json_state)