Read and write a Haystack writable point's priority array via the pointWrite op

Steps

1. Call the pointWrite op with just an id (Ref of the writable point) to read the current priority array; the response returns one row per level with level (1-17, where 17 is the default/relinquish-default level), levelDis, val, and who.
2. To write a value, send a grid with id, level (1-17, with level 8 requiring an explicit duration; level 17 is the default/fallback level and is itself writable), val (or null to release that level), and optionally who to attribute the write.
3. Reserve level 1 for the highest-priority emergency overrides, and use levels 2-7 when an automated routine (e.g., a demand-response energy program) needs to trump a user's manual override at level 8.
4. When writing to level 8 (manual override), always include a duration Number with a duration unit so the override automatically relinquishes back to auto once the timer expires.
5. To release a level so the next-highest non-null level takes control, write val as null at that level rather than deleting the row; a pointWrite response grid is always empty, whether the call was a read or a write.
6. Re-read the priority array after writing to confirm resolution: the effective output is resolved by scanning from level 1 down to level 17 (relinquish default) and using the first non-null val found.