Handle more variations in private index html to improve hash collection

[matteius]

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The issue

Fixes #5894

The fix

I installed a local nexus server, uploaded packages and explored how the index is laid out, and then refactored the hash collector to work with both this and the pytorch style index.

Handles other edge cases around package names with dots.

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 #.