(gazelle) Delete py_library and py_test targets with missing srcs

Followup to https://github.com/bazel-contrib/rules_python/pull/3046#issuecomment-3094797158.

We've merged #3046 which will delete `py_binary` targets with missing srcs - let's now expand that to include `py_library` and `py_test` targets.

@yushan26 did you want to take this on?

Start by reviewing the implementation and tests from pull request #3046, which added deletion for py_binary targets with missing srcs. Extend the same behavior to py_library and py_test targets, then run the related Gazelle tests and confirm those targets are deleted when their srcs are missing.

Vom Indexierungsmodell aus dem Issue-Text verfasst.