feat(typing): add type annotations to whoosh.util.text - #175

Beautiful work, @webdevsamran — this is exactly what #173 asked for, and I love the extra care: the byte(i)/defensive coercions in the prefix helpers and the from __future__ import annotations are all the right calls. 🎉

One thing worth a note (nothing you did wrong): giving rcompile a real return type is a good change, and it did its job — it immediately surfaced two latent inaccuracies elsewhere that the ty pre-commit hook then flagged:

• whoosh.analysis.analyzers annotated several expression params as str, even though they accept str | re.Pattern[str] (the tokenizers already got this right).
• a couple of whoosh.qparser.dateparse parser classes call Pattern.match(text, pos) where text/pos were unannotated.

Rather than send those back to you (they're outside whoosh.util.text), I pushed a small companion commit to your branch (d7b2e04): I tightened rcompile to re.Pattern[str], widened the analyzer expression params to str | re.Pattern[str], and annotated the dateparse parse() signatures. ty, ruff, and the full test suite are all green locally (103 passing across dateparse/analysis/sorting). Once CI confirms, I'll merge.

Thank you for a genuinely clean, well-described PR — this is your second solid contribution and it's very appreciated. If you enjoyed this, #121 has plenty more whoosh.util.* and analysis modules in the same vein whenever you're up for it.