close

Requests terminal close. Idempotent, and returns at once without proving teardown completed.

The request immediately rejects later commands and starts the same close observed by closeAndAwait. Every outstanding call is completed, the workers are stopped, the decoders and the device are closed on their owning threads, and those threads are released, but none of that is a postcondition of this non-suspending return. Use closeAndAwait when completion or failure matters.