Calculate a driver schedule

Queues a driver-scheduling run (DSP) and returns its activity id. DSP assigns the org's drivers (from their shifts) to fixed multi-stop loads (orders grouped by delivery day and optimization_parameters.sequence_group) over days delivery days from plan_from, under US DOT hours of service, at the lowest cost, sending what own drivers can't cover to the request's fallbacks. The first commit_days days are saved as routes with planned drivers, replacing that day's earlier DSP routes; commit_days=0 is a dry run that saves nothing. driver_clocks injects drivers' hours-of-service state; clocks from earlier committed runs persist. Result load IDs are <delivery-date>:<sequence-group>, using the planning time zone. Poll GET /v1/activities/{id} until status is SUCCESS or FAILED; the schedule is in result.