Change where we cache the package finder to alleviate issue collecting hashes with multiple indexes.

[matteius]

Fixes #6249

The fix

My theory is that caching the package finder property was wrong, because it uses other attributes which may yield multiple finders in the case of multiple indexes. So I moved the point at which the caching takes place.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[matteius]

If this truly fixes it -- well cache was introduced in 3.9 but in October (~8 days away) we can actually drop Python 3.8 support because it goes EoL.

[matteius]

After reviewing the old index compatibility finder patch, I see I missed porting over part of the old patch. First order of business is seeing if this fixes the issue --if so I can backport this patch when I have to redo the patching for 24.2