feat: backfill coverage through the serialized publisher

[helly25]

Recover unpublished coverage from an existing CI run through the normal serialized publisher, without rerunning tests. Preserve the original report identity and existing release dispatch behavior.

AG;DR

• Adapt Allow coverage backfill through the serialized publisher xff#886 with optional source_run_id. This selects coverage publication even without coverage_refresh; leaving both unset still publishes releases, and coverage_refresh=true alone still refreshes metadata.
• Accept positive numeric IDs for completed runs of this repository’s .github/workflows/ci.yml. Fetch original timestamps, tested SHA, attempt, event, branch and PR identity from GitHub. Automatic events resolve their original attempt even if a newer retry exists; manual backfill selects the current completed attempt.
• Reuse fix: publish coverage independently of unrelated CI failures #139’s successful Rust coverage job gate, immutable attempt-specific artifact download, archival, freshness selection, and shared publication queue. No untrusted checkout or execution.
• Tests execute the resolver shell with original PR/main metadata, invalid IDs/attempts, incomplete or unrelated workflows, and routing combinations. Existing tests cover artifact naming, job eligibility, archive preservation, late arrivals, and phase preference.
• fix: publish coverage independently of unrelated CI failures #139 is merged. This PR targets main and is synchronized with a50f2ae; no outstanding parent dependency.
• Validation: all 60 Python tests pass on synchronized pushed head 8e5f49a. Applicable pre-commit hooks and replacement CI 35466897043 passed, including the final done gate, against main a50f2ae. fix: publish coverage independently of unrelated CI failures #139 main CI 35466770491 also succeeded.
• Uses existing bash/gh/jq and Python standard library. No new files or dependencies. Artifacts must remain available; expired artifacts cannot be recovered, and no historical backfill is automatically dispatched.