[hood]

Closes #2240

Summary

• char.match now uses a 256-entry lowercase table: LOWER[a] == LOWER[b].
• char.is_semantic_index reads both bytes with one string.byte call and checks the alpha/ALPHA/digit tables directly, without going through the helper functions.

The public char.* helpers are unchanged.

Data

CPU time, best of 20. Benchmark in #2236.

Metric	Before	After
matcher.match x60k	44.9 ms	27.2 ms (-39%)
get_entries, 6k items, isIncomplete	69.9 ms	62.2 ms (-11%)
get_entries, 20k items, isIncomplete	237.7 ms	208.5 ms (-12%)

Same results

Checked against the current char.lua and matcher.lua:

Check	Cases	Differences
char.match: all byte pairs, including nil	66,049	0
is_semantic_index: all 2-byte strings, index 0..3	262,144	0
matcher.match: random words x inputs x matching options (same score and matches)	210,000	0

Testing

All 73 specs pass, luacheck reports 0 warnings, and touched files are formatted with stylua.

[hrsh7th]

thank you.