Add a fast path for ASCII strings

This optimization is based on a few assumptions:

  - Most strings are ASCII only.
  - Most strings had their coderange scanned already.

If the above is true, then by checking the string coderange, we can
use a much more streamlined function to encode ASCII strings.

Before:

```
== Encoding twitter.json (466906 bytes)
ruby 3.4.0preview2 (2024-10-07 master 32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json   140.000 i/100ms
                  oj   230.000 i/100ms
           rapidjson   108.000 i/100ms
Calculating -------------------------------------
                json      1.464k (± 1.4%) i/s  (682.83 μs/i) -      7.420k in   5.067573s
                  oj      2.338k (± 1.5%) i/s  (427.64 μs/i) -     11.730k in   5.017336s
           rapidjson      1.075k (± 1.6%) i/s  (930.40 μs/i) -      5.400k in   5.025469s

Comparison:
                json:     1464.5 i/s
                  oj:     2338.4 i/s - 1.60x  faster
           rapidjson:     1074.8 i/s - 1.36x  slower

```

After:

```
== Encoding twitter.json (466906 bytes)
ruby 3.4.0preview2 (2024-10-07 master 32c733f57b) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
                json   189.000 i/100ms
                  oj   228.000 i/100ms
           rapidjson   108.000 i/100ms
Calculating -------------------------------------
                json      1.903k (± 1.2%) i/s  (525.55 μs/i) -      9.639k in   5.066521s
                  oj      2.306k (± 1.3%) i/s  (433.71 μs/i) -     11.628k in   5.044096s
           rapidjson      1.069k (± 2.4%) i/s  (935.38 μs/i) -      5.400k in   5.053794s

Comparison:
                json:     1902.8 i/s
                  oj:     2305.7 i/s - 1.21x  faster
           rapidjson:     1069.1 i/s - 1.78x  slower
```

0 files changed, 0 insertions, 0 deletions