Periodically extends a lease while a job is being processed.

Per QuiCK paper Algorithm 3: Workers should extend leases in parallel with job execution to prevent long-running jobs from losing their lease.

Behavior

• Started via start/5 which spawns a linked process
• The process loops, extending the lease at regular intervals
• Stopped via stop/1 when the job completes (sends :stop message)
• Uses spawn_link so the extender dies if the parent job process crashes
• Extension failures are logged but don't stop the loop - the job may still complete in time before the lease expires
• If the lease cannot be extended (e.g., already expired), logging occurs but execution continues

Timing

By default, the extender runs every lease_duration / 3 milliseconds and extends the lease by lease_duration milliseconds. This ensures the lease is extended well before expiration even if one extension attempt fails.