chore: enforce usage of to_ascii_lowercase_cow

[minht11]

Summary

Basically the same ideas as oxc-project/oxc#5586.
Enforce usage of biome_string_case::StrExtension::to_ascii_lowercase_cow with Clippy to minimize memory allocation.

Test Plan

All existing tests should pass.

[arendjr]

I didn’t realise this was so easy with Clippy 👍 And I do like we use our own utils indeed.

[codspeed-hq]

CodSpeed Performance Report

Merging #4014 will improve performances by 9.06%

_{Comparing minht11:chore/enforce-to_ascii_lowercase_cow-usage (70c37db) with main (1a87927)}

Summary

⚡ 1 improvements
✅ 106 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	minht11:chore/enforce-to_ascii_lowercase_cow-usage	Change
⚡	db_17847247775464589309.json[cached]	13.9 ms	12.8 ms	+9.06%

[dyc3]

Whoops, I didn't see the check deps job failure. Fixed in #4016