Summary

• Update vendored simdjson from v0.5.0 to v4.6.1, raise C++ standard to C++17
• Raise minimum Ruby from 2.6 to 3.2, CI matrix: Ruby 3.2, 3.3, 3.4, 4.0
• Modernize gemspec: explicit file list, metadata, move dev deps to Gemfile
• Update RuboCop to 1.x, GitHub Actions to checkout@v4
• Fix missing optimization flags in CXXFLAGS (based on @Watson1978's Fix performance on Ruby 3.0 #24)

Details

simdjson C++ library

• Submodule URL: lemire/simdjson → simdjson/simdjson (upstream migration)
• Submodule version: v0.5.0 → v4.6.1
• simdjson.h must now be included before ruby.h to avoid snprintf macro conflict

Performance fix

• Incorporated the fix from @Watson1978's Fix performance on Ruby 3.0 #24: Ruby 3.0+ no longer includes $(optflags) in CXXFLAGS automatically, causing simdjson to compile without -O2. Adding $(optflags) $(debugflags) restores proper optimization.

Ruby / Gem

• required_ruby_version: >= 2.6 → >= 3.2
• Gemspec: replaced git ls-files with Dir.glob, removed dead bindir/executables, added rubygems_mfa_required metadata
• Dev dependencies moved from gemspec to Gemfile (modern Bundler convention)

CI / Tooling

• actions/checkout@v2 → @v4
• Ruby matrix: [2.6, 2.7, 3.0] → [3.2, 3.3, 3.4, 4.0]
• RuboCop 0.89 → 1.x (require: → plugins:, NewCops: disable)

Test plan

• bundle exec rake (clobber → compile → test) — 10 tests, 0 failures
• bundle exec rubocop --fail-level=W — 0 offenses
• bundle exec rake bench — runs without crashes
• gem build simdjson.gemspec — produces correct gem with only necessary files
• CI passes on Ruby 3.2, 3.3, 3.4, 4.0

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