perf: avoid regex re-compile

[trim21]

Summary

found re.findall and re.sub usage in starlette module, we should always pre-compile regex pattern if it's possible.

Althrough re has a built-in cache, but it has size limit and for project using many regex it still may be invalidated and pattern get unnecessary re-compile.

There is still one case in

starlette/starlette/_utils.py

Line 88 in 1131b3c

route_path = re.sub(r"^" + root_path + r"(?=/|$)", "", scope["path"])

It's not a simple case so I didn't touch it.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Kludex]

Thanks! 🙏