fix: backfill nested pagination

[MkDev11]

Summary

Fix backfill pagination for nested GitHub GraphQL connections used by miner scoring inputs.

Root cause: repo backfill paginated parent PR/issue pages, but treated capped nested reviews, labels, and label timelineItems connections as complete. Historical rows could silently miss PR reviews and label events before webhook registration.

Changed behavior:

• paginate PR reviews beyond the initial nested page
• paginate PR and issue current labels beyond the initial nested page
• paginate PR and issue labeled/unlabeled timeline events beyond the initial nested page

Preserved behavior:

• parent PR/issue backfill pagination and date cutoff behavior are unchanged
• live webhook ingestion remains unchanged
• single-page nested responses without nested pageInfo still persist from the initial nodes without extra fetches

Related Issues

Closes #9

Type of Change

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

Testing

• npm test
• npm run format:check
• npm run lint
• npm run build
• git diff --check

Live GitHub API/E2E backfill was not run locally; coverage uses deterministic mocked GraphQL responses for paginated and non-paginated nested connections.

Checklist

• I have read the Contributing Guide
• Code builds without errors
• New and existing tests pass (if applicable)
• Documentation updated (if applicable)
• No unnecessary dependencies added

[anderdc]

Closing alongside #9 — see issue note. Scope is also disproportionate (+691/-11 for full nested cursor pagination across three connections) relative to the data the mirror scorer actually consumes.