fix(issue-discovery): zero per-repo issue fields for repos absent this round

[jaytbarimbao-collab]

Summary

_finalize_repo_issue_scores only rewrote the repos seen this round (sorted(set(repo_acc) | set(open_counts))), but _roll_up_issue_totals sums over all evaluation.repo_evaluations. A repo issue-scored in a prior round that is absent this round — e.g. an evaluation restored from the cache after an OSS PR-fetch failure (store_or_use_cached_evaluation), which carries prior-round repo_evaluations — kept its stale per-repo issue values, and those got summed back into the round-level totals. This inflates total_solved_issues / issue_discovery_score / is_issue_eligible in stored data, CLI miner score, analytics, and the cross-round cache.

The no-issues path (_clear_issue_discovery_fields) already zeroes every repo_evaluation, which is the intended contract; the scoring path had drifted from it. This extracts the per-repo reset into a shared _reset_repo_issue_fields helper and applies it on the scoring path to any repo not seen this round, before the roll-up.

Current-round emission allocation reads the freshly-rebuilt issue_discovery_issues list, so this is a stored-data / reporting correctness fix, not an emissions change.

Related Issues

Fixes #1610

Type of Change

• Bug fix

Testing

• Tests added — TestFinalizeStaleRepoReset::test_repo_absent_this_round_is_zeroed_not_summed asserts a repo absent this round is zeroed and not summed into the round totals. Fails on test before the fix (repo stays at 7 solved / 8.12 score, roll-up inherits it), passes after.
• Full suite green (965 passed), ruff + pyright clean.

Checklist

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

[jaytbarimbao-collab]

@anderdc @LandynDev fixes #1610. _finalize_repo_issue_scores only rewrites repos seen this round, but _roll_up_issue_totals sums all repo_evaluations — so a repo issue-scored in a prior round and restored from the eval cache keeps stale per-repo values that inflate the round totals. The no-issues path (_clear_issue_discovery_fields) already does the full reset; this shares that reset onto the scoring path. Stored-data/reporting correctness, not an emissions change. +regression test.