✨ feat(mq-lang): add sort_natural for numeric-aware natural sorting

[harehare]

Summary

Sorts arrays so embedded digit runs compare numerically instead of lexicographically (e.g. "file2" before "file10"), similar to GNU sort -V. Implemented in builtin.mq on top of sort_by using scan/lpad, with type-checker registration in mq-check.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor
• 📝 Documentation
• ⚡ Performance
• ✅ Test
• 📦 Build / dependencies
• 👷 CI

Checklist

• I ran cargo fmt and cargo clippy and addressed any warnings
• I ran just test-all and all tests pass
• I added or updated tests covering this change
• I updated relevant documentation (/docs, crate README.md) if needed
• I added a changelog entry if this is a user-facing change

Additional Context

[codspeed-hq]

Merging this PR will improve performance by 15.33%

⚡ 1 improved benchmark
✅ 30 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	eval_macro_expansion_simple	113 µs	98 µs	+15.33%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing feat/sort-natural (af780da) with main (859437e)}