refactor(plugin): replace deprecated pkg_resources with importlib.metadata

- Use distributions() in __get_installed_packages for installed packages
- Use packaging.requirements.Requirement, drop pkg_resources dependency
- __standardize_pkg_name: normalize dots to underscores (PEP-style)
- Keep max version when multiple distributions exist for same package

Made-with: Cursor

requirements.in

@@ -1,4 +1,3 @@
-setuptools
 Cython~=3.1.2
 pydantic>=2.0.0,<3.0.0
 pydantic-settings>=2.0.0,<3.0.0