Clarify that arbitrary equality is supposed to be case insensitive

Not currently. But issues do come up over time:

The discussion Are Developmental releases a type of pre-release? resulted in the spec being clarified: Clarify that dev releases are considered pre-releases when handling them by brettcannon · Pull Request #1857 · pypa/packaging.python.org · GitHub.

The discussion Proposal: Intersect and Disjoint Operations for Python Version Specifiers eventually led me to update packaging: PEP 440 handling of prereleases for `Specifier.contains`, `SpecifierSet.contains`, and `SpecifierSet.filter` by notatallshaw · Pull Request #897 · pypa/packaging · GitHub.

The Python packaging specification is massive, with a rich history, and full of edge cases.