[Fix] PR review notifications are lost during pull request creation

[roomote-roomote]

​Opened on behalf of @daniel-lxs. View the task or mention @roomote-roomote for follow-up asks.

What changed

• Retry the idempotent task-to-pull-request association write and surface the error when the bounded retry budget is exhausted.
• Retry review-notification association lookup briefly so a webhook arriving while the association is committing can still schedule the notification.
• Add deterministic coverage for the concurrent write/read race, transient and persistent write failures, bounded unrelated lookups, and single scheduling.

Why this change was made

A review webhook could arrive after pull request creation succeeded but before its task association became visible. The initial lookup then treated the pull request as unrelated and permanently discarded the notification.

Impact

Review activity arriving during pull request association persistence is retained and scheduled once. Unrelated pull requests still exit after a short bounded lookup, and the change requires no schema migration or durable event system.

Package-wide SDK lint remains blocked by three pre-existing unused-disable warnings in untouched files; lint on all touched files passes.

[roomote-community]

No code issues found. See task

_{Reviewed 9c15424}

[roomote-roomote]

Closing as superseded by #1262, which covers the same association race with queue-backed bounded reconciliation and deterministic replay deduplication.