Update an equipment downtime by id. This is a full replacement: the window and the whole set of departments and equipment are saved from the request, in request order, so omitting `departments` clears them. The same rules as create apply: the end cannot be earlier than the start, each department must exist and be listed once, and each piece of equipment must be in its department and be listed once for it. The server fills `departmentName` and `equipmentName` from the records.

Details of an equipment downtime to save. An update replaces the whole downtime: its window and its whole set of departments and equipment are saved from the request, so omitted departments are cleared. The shape matches what GET /equipment-downtimes/{id} returns, so a fetched downtime can be sent back; the read-only members id, deleted, departmentName, allEquipment and equipmentName are ignored, and the server fills the names from the department and equipment.

A window of time when departments, or chosen equipment within them, are unavailable for scheduling.