forward() only popped _stream_gens on normal completion, so cancelled,
timed-out, or preempted requests leaked their generator and skipped the
finally block that unlinks the temp WAV files. Implement
on_requests_finished to close each finished generator, which raises
GeneratorExit inside it and triggers the existing cleanup.
Signed-off-by: Yueqian Lin <linyueqian@outlook.com>
Yueqian Lin
123dfc0772