runmat-test-runner-execution

This crate is the narrow dependency-direction bridge between RunMat's test coordinator and its portable execution scheduler.

runmat-test and runmat-test-runner remain authoritative for discovery, fixture lifecycle, retries, cancellation policy, events, results, artifacts, reporters, and coverage. runmat-execution-runner remains authoritative for execution scopes, pools, resource admission, attempts, worker fencing, and result commit. ExecutionWorkerBackend maps one exact test attempt onto that scheduler without teaching either domain the other's semantics.

The same adapter wraps native process/session backends and browser Web Worker backends. TestAttemptWorkload is the encrypted remote payload: it binds the complete immutable plan and frozen source snapshot to the exact ProgramRevision, selected TestId, and attempt number. Remote results return the canonical WorkerExecution, so ordering, reporting, artifacts, and coverage are identical to local execution.