Use JSON.generate instead of Yajl.dump

[Watson1978]

What does this PR do?

Recently, Ruby's JSON has huge improvement and it is much faster.
Ref. https://byroot.github.io/ruby/json/2024/12/15/optimizing-ruby-json-part-1.html

So, this PR will change yajl-ruby to Ruby's JSON.

Motivation

Improve performance by using Ruby's JSON

Additional Notes

Please refer following benchmark code and result.

envronment

• Ruby: 3.4.4
• OS: Linux 6.14.6-2
• Compiler: gcc 15.1.1

benchmark

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'benchmark-ips'
  gem 'json'
  gem 'yajl-ruby'
end

require 'json'
require 'yajl'
require 'yajl/version'

puts "* JSON version: #{JSON::VERSION}"
puts "* Yajl version: #{Yajl::VERSION}"

json = '{"a":"Alpha","b":true,"c":12345,"d":[true,[false,[-123456789,null],3.9676,["Something else.",false],null]],"e":{"zero":null,"one":1,"two":2,"three":[3],"four":[0,1,2,3,4]},"f":null,"h":{"a":{"b":{"c":{"d":{"e":{"f":{"g":null}}}}}}},"i":[[[[[[[null]]]]]]]}'
data = JSON.parse(json)

Benchmark.ips do |x|
  x.report('Yajl.dump') { Yajl.dump(data) }
  x.report('JSON.generate') { JSON.generate(data) }

  x.compare!
end

result

$ ruby tmp.rb
* JSON version: 2.12.2
* Yajl version: 1.4.3
ruby 3.4.4 (2025-05-14 revision a38531fd3f) +PRISM [x86_64-linux]
Warming up --------------------------------------
           Yajl.dump    34.964k i/100ms
       JSON.generate   120.598k i/100ms
Calculating -------------------------------------
           Yajl.dump    345.056k (± 2.8%) i/s    (2.90 μs/i) -      1.748M in   5.070452s
       JSON.generate      1.212M (± 1.6%) i/s  (824.89 ns/i) -      6.150M in   5.074868s

Comparison:
       JSON.generate:  1212286.6 i/s
           Yajl.dump:   345056.0 i/s - 3.51x  slower