Normalize extras when evaluating PEP 508 markers (#915)
## Summary
We always normalize extra names in our requirements (e.g., `cuda12_pip`
to `cuda12-pip`), but we weren't normalizing within PEP 508 markers,
which meant we ended up comparing `cuda12-pip` (normalized) against
`cuda12_pip` (unnormalized).
Closes https://github.com/astral-sh/puffin/issues/911.