win-wasapi Improve default device handling

Remove lastNotifyTime throttle. Could ignore last device notification.
Will bring back if necessary, but seemed like overkill.

Make isInputDevice const for safety.

Make isDefaultDevice atomic. Allows it to be accessed simultaneously
from settings and notification callback threads. Race between setting
change in OBS and Windows is not a problem, a signal will be sent after
both to consolidate. Worst that should happen is a redundant reconnect
cycle.

Only read/write default_id from notification callback for thread safety.