feat: Distinguish file-level vs release-level yanking (PEP 592)

[Ashutosh0x]

Summary

This PR implements proper distinction between file-level and release-level yanking as specified in PEP 592, addressing #13755.

Changes

Core Logic (src/pip/_internal/resolution/resolvelib/factory.py)

The yanking logic has been updated to properly handle two distinct scenarios:

1. File-level yanking: When individual files are yanked but not all files for a version, only those specific yanked files are excluded. Other non-yanked files from the same version can still be selected.

2. Release-level yanking: When ALL files for a version are yanked, the version is considered "yanked" and the pinned version exception (== or ===) applies.

Implementation Details

• Group candidates by version to determine if a version has release-level yanking (all files yanked) or file-level yanking (some files yanked)
• For file-level yanking: exclude only the yanked files, allow non-yanked files
• For release-level yanking: apply the PEP 592 "pinned exception" - only allow if the specifier explicitly pins to that version
• Track yanked_versions set to identify release-level yanked versions
• Track all_versions_yanked to handle the edge case where all available versions are yanked

Tests

Added comprehensive unit tests in tests/unit/test_yanking.py covering:

• File-level yanking excludes only yanked files
• Release-level yanking detection
• Pinned specifier exceptions for release-level yanking
• Mixed scenarios with both file-level and release-level yanking

Test Data

Added test index tests/data/indexes/partial_yanked/ with scenarios for:

• Version 1.0: file-level yanking (one file yanked, one not)
• Version 2.0: release-level yanking (all files yanked)
• Version 3.0: no yanking

Fixes

Closes #13755

References

• PEP 592 - Adding "Yank" Support to the Simple API

[notatallshaw]

This news item is way too long, keep it to one or two short sentances.

[notatallshaw]

I was inspired to write up #13755 because of the following bug:

• Specifier >1 and a yanked release 2.0 and a pre-release 3.0rc1, in this case 3.0rc1 should be selected

The point is to make sure this bug is fixed and yanking follows the specification. Please, at a minimum, add this test case.