Fix O(N) global scan in artifact-version delete

[joaquinhuigomez]

Summary

• Replaces the global depaginate(list_artifact_versions, only_unused=True) membership check in _delete_artifact_version with a targeted query that filters by the specific artifact version ID (id=artifact_version.id, only_unused=True, size=1)
• This avoids re-listing every unused artifact version on each delete call, which caused O(N) paginated API requests per deletion (see Performance bug: artifact-version delete does global only_unused depagination per delete #4684 for profiling data showing ~41s per delete reduced to ~0.6s)

Test plan

• Verify Client.delete_artifact_version() still raises ValueError for in-use artifact versions
• Verify unused artifact versions are deleted successfully
• Confirm paginated GET calls are reduced from O(N) to 1 per deletion

Fixes #4684

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[bcdurak]

@joaquinhuigomez thank you for the PR! Can you please sign the CLA? We will take a look as soon as possible.