perf: Avoid recompiling regexes

[dzbarsky]

We can compile these once at package scope instead. This is a slight perf improvement on a medium repo.

I removed some unused code while I was here.

[DavidZbarsky-at]

Example:

[dzbarsky]

@vladmos can you please take a look at this one?

[zbarsky-openai]

@vladmos gentle ping on this one :)