[ruby/prism] Optimize ruby visitor

`compact_child_nodes` allocates an array. We can skip that step by simply yielding the nodes.

Benchmark for visiting the rails codebase:

```rb
require "prism"
require "benchmark/ips"

files = Dir.glob("../rails/**/*.rb")
results = files.map { Prism.parse_file(it) }
visitor = Prism::Visitor.new

Benchmark.ips do |x|
  x.config(warmup: 3, time: 10)

  x.report do
    results.each do
      visitor.visit(it.value)
    end
  end
end

RubyVM::YJIT.enable

Benchmark.ips do |x|
  x.config(warmup: 3, time: 10)

  x.report do
    results.each do
      visitor.visit(it.value)
    end
  end
end
```

Before:
```
ruby 3.4.8 (2025-12-17 revision https://github.com/ruby/prism/commit/995b59f666) +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          2.691 (± 0.0%) i/s  (371.55 ms/i) -     27.000 in  10.089422s
ruby 3.4.8 (2025-12-17 revision https://github.com/ruby/prism/commit/995b59f666) +YJIT +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          7.278 (±13.7%) i/s  (137.39 ms/i) -     70.000 in  10.071568s
```
After:
```
ruby 3.4.8 (2025-12-17 revision https://github.com/ruby/prism/commit/995b59f666) +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          3.429 (± 0.0%) i/s  (291.65 ms/i) -     35.000 in  10.208580s
ruby 3.4.8 (2025-12-17 revision https://github.com/ruby/prism/commit/995b59f666) +YJIT +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                         16.815 (± 0.0%) i/s   (59.47 ms/i) -    169.000 in  10.054668s
```

~21% faster on the interpreter, ~56% with YJIT

https://github.com/ruby/prism/commit/bf631750cf

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