Normalize names per PEP503; update test fixtures

[eloquence]

Fixes #479

pyproject.toml allows dependency names to be specified in all permissible variations before they get normalized per PEP 503 in the lockfile. This wasn't previously taken into account when parsing requirements. (Dependency names can also appear inside of quotation marks, but that's already normalized when parsing the TOML.)

In principle, we shouldn't need to normalize the names we encounter in poetry.lock itself, but since the format is not supposed to be considered stable, we're erring on the side of caution.

Test plan

• Follow the STR in #479
• [x] Confirm that the issue is fixed

[eloquence]

Thanks @cfm , I like and accepted that change. As a nice example of CI drift, CI started failing after that due to this PR not having been rebased in a while -- have done so as well.