Add CI checks for PythonBundles

[Flamefire]

Based on the last confcall this adds CI checks to ensure the new rules:

• Single extensions should be PythonPackage
• Python packages which (usually) are build dependencies only should not be extensions of other bundles

EasyConfigs named *-bundle* are explicitely ignored.

Running a check over all existings ECs:

• 549 single-extension bundles
• 139 with build dependencies. Most commonly wheel, setuptools, packaging, pyproject-metadata, hatchling

As a companion I can enhance PythonPackage to support package_name defaulting to name. This will be used a) for pip checks and b) to add an extension to modules.
Required decision: I'd only add it as an extension when it is different to name.

• Avoids cluttering module spider/show/av which would show it twice as the module and as an extension of itself which I don't see any benefit
• Is somehow backwards compatible in not adding extensions for existing PythonPackage modules

I can also look into automatically converting the existing single-extension bundles to make it easier for contributors to do updates. I'd expect to be able to use a simple script for that to do all in one go.

Initial draft created by local AI agent including the list of build-dependencies.