When a file sliced for the wrong nozzle size is dispatched, the printer
goes IDLE -> PREPARE -> FAILED without ever entering RUNNING. Completion
detection required prev=RUNNING or _was_running=True, so on_print_complete
never fired and the queue item stayed at "printing" forever -- blocking
every subsequent pending item for that printer (check_queue seeds
busy_printers from any row in 'printing').
Fire completion on FAILED from PREPARE or SLICING too. Restricted to
those two pre-print states so a stale FAILED on first connection
(prev=None) still can't accidentally advance an unrelated queue item.
Also populate PrintQueueItem.error_message from the current HMS error
list via the existing hms_errors.py lookup, so users see e.g.
"[0500_4038] The nozzle diameter in sliced file is not consistent
with the current nozzle setting" instead of a blank failure reason.
maziggy
08601b4772