This PR modifies the PEP 440 and PEP 508 crates to pass CI, primarily by
fixing all lint violations.
We're also now using these crates in the workspace via `path`.
(Previously, we were still fetching them from Cargo.)
This PR copies over the `pep440-rs` crate at commit
`a8303b01ffef6fccfdce562a887f6b110d482ef3` with no modifications.
It won't pass CI, but modifications will intentionally be confined to
later PRs.
