✨ feat(mq-lang): add tally, frequencies_by, comp, juxt, complement builtins

[harehare]

Summary

Adds frequency-counting helpers (tally/frequencies_by) alongside the existing group_by/sort_by/*_by family, and function-composition utilities (comp/juxt/complement) enabled by mq's first-class functions. comp and juxt take a variadic list of functions.

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 27.79%

⚡ 1 improved benchmark
✅ 30 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	eval_macro_expansion_simple	132.4 µs	103.6 µs	+27.79%

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/functional-builtins (2fa45ee) with main (3b042e4)¹}

Footnotes

1. No successful run was found on main (de94b5b) during the generation of this report, so 3b042e4 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩