Disuse pkg_resources in favor of importlib.metadata

[dairiki]

Pkg_resources is deprecated. Importlib.metadata is the new standard way of dealing with distribution metadata: entry points, versions, etc.

This PR eliminates our usage of pkg_resources in favor of importlib.metadata (or importlib_metadata for python < 3.10 — in this PR we use importlib.metadata.packages_distributions() which is only available in 3.10.)

Issue(s) Resolved

This would have sort of fixed the issue noted in #1058 having to do with the misspelling of a dependency. (The real problem there was the misspelling; however, using the same distribution grokking machinery as python itself uses helps minimize weirdness due to differences in behavior between the import system and the introspection system.)

Related Issues / Links

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

[yagebu]

LGTM :)