Make isolate re-use the same agent as long as the connection is open

[isidentical]

In the current implementation, we just receive a single callable, call it, and exit from the agent. But since each connection can actually execute multiple callables, it is really inefficient to re-start the agent process for no reason.

isolate/src/isolate/backends/connections/ipc/agent.py

Lines 107 to 137 in 6587d96

	# TODO(feat): this should probably run in a loop instead of
	# receiving a single function and then exitting immediately.
	with child_connection(serialization_backend_name, address) as connection:
	print(f"[trace] Created child connection to {address}")
	callable = connection.recv()
	print(f"[trace] Received the callable at {address}")
	result = None
	did_it_raise = False
	try:
	result = callable()
	except BaseException as exc:
	result = exc
	did_it_raise = True
	finally:
	try:
	connection.send((result, did_it_raise))
	except BaseException:
	if did_it_raise:
	# If we can't even send it through the connection
	# still try to dump it to the stderr as the last
	# resort.
	import traceback
	assert isinstance(result, BaseException)
	traceback.print_exception(
	type(result),
	result,
	result.__traceback__,
	)
	raise