It turns out that for ASCII identifiers, this is nearly 2x faster:
```
Parser/before time: [15.388 ns 15.395 ns 15.406 ns]
Parser/after time: [8.3786 ns 8.5821 ns 8.7715 ns]
```
## Summary
I noticed that we have a few hot comparisons that involve called
`s.to_lowercase()`. We can avoid an allocation by comparing characters
directly.
In hindsight, `ruff_python` is too general. A good giveaway is that it's actually a prefix of some other crates. The intent of this crate is to reimplement pieces of the Python standard library and CPython itself, so `ruff_python_stdlib` feels appropriate.
Micha Reiser
Charlie Marsh