[un-def]

_prepare_startup_context ran on every PROVISIONING and PULLING tick and returned early whenever the runner submission had to wait for other jobs: replica provisioning, the router IP, or referenced group IPs. The early return also skipped the status handlers' own work: copying the instance provisioning data into the job, failing the job when its instance is terminated, the provisioning timeout, and shim polling. With replica IP refs on newly provisioned instances, jobs waited for IPs that only the skipped copy would set, so the run stayed in provisioning forever.

• Replace _prepare_startup_context with _prepare_runner_submission, called right before the runner submission once the runner is up.
• Load volumes and interpolate secrets in the shim branch, which needs the interpolated registry_auth. The shim no longer waits for other jobs, so the image pull starts earlier.
• Terminate workers whose router failed or did not get an IP in time in _terminate_if_router_unavailable, before both statuses as before.
• Wait for every job in the replica to have a hostname, not only provisioning data, since shim submission no longer ensures it.
• Drop the unused secrets parameter of _submit_job_to_runner.

Fixes: #4331