✨ feat(mq-lang): add ascii_downcase and ascii_upcase builtin functions

[harehare]

Adds jq-compatible ascii_downcase/ascii_upcase, which fold only ASCII letters (A-Z/a-z) and leave other Unicode characters untouched, unlike the existing downcase/upcase which use full Unicode case folding.

[codspeed-hq]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

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_{Comparing feat/ascii-downcase-upcase (77bf2bc) with main (eaaca7b)¹}

Footnotes

1. No successful run was found on main (d556a74) during the generation of this report, so eaaca7b was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩