fix: sync pr_state for stale-merged PRs excluded from scoring

[Crystora]

Summary

A PR stored as OPEN stays stuck as OPEN in pull_requests if it gets merged on GitHub after the 35-day lookback window has already passed. The miner API and dashboard then keep showing it as open with a stale collateral_score.

Close: #1070

Root cause

should_skip_merged_pr returns True once merged_at is older than the lookback window, and the loop just continues. The PR never enters any bucket, so the old OPEN row never gets refreshed.

#769 fixed the same shape for stale-CLOSED PRs. This adds the MERGED counterpart.

Fix

New stale_merged_pull_requests bucket on MinerEvaluation, paired with a targeted UPDATE (not the bulk upsert) so existing rows get their status synced without touching scoring fields.

File	Change
gittensor/classes.py	Add stale_merged_pull_requests + add_stale_merged_pull_request.
gittensor/utils/github_api_tools.py	Add _maybe_add_stale_merged_pr, called from the merged-PR skip branch.
gittensor/validator/storage/queries.py	Add REFRESH_STALE_MERGED_PR_STATE — UPDATE-only, status fields only, guarded by pr_state != 'MERGED'.
gittensor/validator/storage/repository.py	Add refresh_stale_merged_pr_states.
gittensor/validator/utils/storage.py	Wire the refresh into the existing transaction.

Why UPDATE instead of the bulk upsert #769 used

A stale-MERGED row may already have real scoring fields from an earlier round. The bulk upsert would overwrite them with dataclass defaults. The targeted UPDATE only touches pr_state, merged_at, collateral_score, updated_at, never inserts, and skips rows already at pr_state = 'MERGED'.

No scoring impact

Stale-merged PRs never enter merged_pull_requests, so totals, eligibility, credibility, token score, pioneer math, and emissions are all unchanged.

Test plan

• uv run python -m pytest tests/ — 1418 passed (7 new)
• uv run python -m pyright — 0 errors
• uv run pre-commit run — all hooks pass

New tests:

• tests/validator/test_unscored_stale_prs.py — stale-merged routes to the storage-only bucket, doesn't inflate totals; fresh merged PR is not captured; missing mergedAt is skipped safely.
• tests/validator/utils/test_storage_mirror.py — stale-merged list goes through refresh_stale_merged_pr_states, not the bulk upsert path.

Related

Follow-up to #769.

[anderdc]

Stale-merged only fires when a single miner's scanning has a >35-day gap (PAT lapse, identity change, etc.) and the impact is dashboard-only — no scoring effect. The stale-CLOSED variant in #769 covered the substantially more common case where any user can close a PR at any time. Not pursuing this edge case. Closing.