[PR #1303/877e9e72 backport][3.32] Fix Simple API cache poisoning via ?format=json

[patchback]

This is a backport of PR #1303 as merged into main (877e9e7).

Summary

• Key PythonApiCache on the negotiated media type instead of the raw Accept header so ?format=json and HTML negotiation no longer share a cache entry
• Add a regression test for the uv/pip-style Accept + ?format=json poison case
• Changelog for PyPI simple API returns 500 when BrowsableAPIRenderer is selected (no template_name set) #1302

Test plan

• oci-env test -p pulp_python functional -- -k test_simple_cache -v
• Confirm a ?format=json warm followed by the same Accept without format returns HTML 200 (not 500)

Made with Cursor

[jobselko]

We need to backport pulp/pulpcore#7890 to core 3.105 to fix the lowerbounds.