Inbound wire messages are now delivered FROM the proxy representing the
remote sender, so local actors see a replyable `from`. This enables full
two-way communication across the wire:
- endpoint: deliver send_named/send via proxy (deliver_named/deliver_pid)
instead of sending raw; from_id=0 bypasses proxy for anonymous sends
- proxy: handle deliver_named and deliver_pid to send from within actor
scope (providing from-substitution); cache one owned pid clone per sender
keyed by stable instance_id() to avoid use-after-free when forwarding
reply handles to the endpoint asynchronously
- test: add remote_endpoint_id_test covering the full inbound proxy table /
from-substitution / outbound ID table / send-by-ID round-trip
- test: extend remote_child_endpoint with echo_id actor and send_wire_by_id
to support the new test
