perf(cache): extend shallow-copy cache helpers to mirror PRs

[mkdev5]

Summary

_build_cache_entry and _isolate_for_downstream from #786 only handle legacy PullRequest lists. After copy.copy(evaluation), the three mirror lists (mirror_merged_prs, mirror_open_prs, mirror_closed_prs) remain as shared references — source mutations leak into the cache, successive get() calls share the same ScoredMirrorPR objects, and heavy files[*].head_content / base_content blobs are never stripped.

What changed

• _build_cache_entry — copies each ScoredMirrorPR and its nested MirrorPullRequest (review_summary, labels, linked_issues), sets files = None.
• _isolate_for_downstream — copies each cached ScoredMirrorPR and mutable sub-objects to isolate successive get() calls.
• 4 module-level helpers: _scored_mirror_pr_for_cache, _scored_mirror_pr_isolated, _mirror_pr_copy, _mirror_linked_issue_copy.
• TestMirrorCacheIsolation — 3 tests covering file-blob stripping, store-to-get isolation, and get-to-get isolation.

Related Issues

Closes #696

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Testing

• Tests added/updated
• Manually tested

uv run pytest tests/validator/test_validator_cache_fallback.py  # 9 passed
uv run ruff check gittensor/classes.py tests/validator/test_validator_cache_fallback.py  # All checks passed
uv run ruff format --check gittensor/classes.py tests/validator/test_validator_cache_fallback.py  # Already formatted
uv run pyright gittensor/classes.py tests/validator/test_validator_cache_fallback.py  # 0 errors

Checklist

• Code follows project style guidelines
• Self-review completed
• Changes are documented (if applicable)

[anderdc]

#786 just merged with the legacy-path shallow-copy helpers (_build_cache_entry / _isolate_for_downstream). Please rebase this onto test and scope it down to just the mirror additions on top of those helpers.

Keep: dropping ScoredMirrorPR.files in _build_cache_entry, shallow-copying each ScoredMirrorPR (plus pr / pr.review_summary / pr.labels / pr.linked_issues with their labels) in _isolate_for_downstream, and the mirror-specific tests.

Drop: the rewrite to a single create_lightweight_copy (already replaced), _copy_pull_request_for_cache / _copy_issues (equivalents already in _pr_for_cache / _pr_with_fresh_issues), and the legacy-only test cases #786 already covers.

[mkdev5]

#786 just merged with the legacy-path shallow-copy helpers (_build_cache_entry / _isolate_for_downstream). Please rebase this onto test and scope it down to just the mirror additions on top of those helpers.

Keep: dropping ScoredMirrorPR.files in _build_cache_entry, shallow-copying each ScoredMirrorPR (plus pr / pr.review_summary / pr.labels / pr.linked_issues with their labels) in _isolate_for_downstream, and the mirror-specific tests.

Drop: the rewrite to a single create_lightweight_copy (already replaced), _copy_pull_request_for_cache / _copy_issues (equivalents already in _pr_for_cache / _pr_with_fresh_issues), and the legacy-only test cases #786 already covers.

@anderdc can you please review the update?

[anderdc]

Closing as duplicate of #824