Faster flaky-test back-marking via a commit-scoped bloom filter

Flaky-test back-marking is now scoped by commit SHA on the ClickHouse test runs table, which engages the table’s bloom filter and prunes scans to only the granules holding that commit’s runs. This dramatically reduces the rows, bytes, and memory needed by mark_test_case_runs_as_flaky, so historical flakiness detection no longer shows up on the “Slow ClickHouse query” alerts.