mypy

739a6524 - [mypyc] Add `librt.strings.isalnum` codepoint primitive (#21509)

[mypyc] Add `librt.strings.isalnum` codepoint primitive (#21509) 3rd PR for https://github.com/python/mypy/issues/21418, mirroring `librt.strings.isdigit`. Measured on a microbenchmark this is roughly 30-40% faster for a char