feat: one-way calls — Client::notify + Server skips the empty reply (7f)

[Kinflou]

For _return: None schema functions: fire-and-forget, no response frame.

Client::notify<P>(call_id, &P) -> Result<(), RuntimeError>	frames + sends a request, returns without a recv. Ok(()) = the frame left the transport, nothing more. Request ids stay monotonic across mixed call / notify.
Server::serve_one	after dispatch, if the generated dispatcher wrote no Envelope, there's nothing to reply — skip encode_response + send. Any real envelope is ≥ 1 tag byte, so "empty" is unambiguous. No wire or contract change.
InMemory::try_recv	non-blocking receive — single-threaded pumping, and asserting a one-way call drew no reply.

Test

tests/oneway_roundtrip.rs — a Log { record(line: str); } stand-in for what comline-rust emits for a no-return function: the client notifys twice, the server pumps both frames and replies to neither, try_recv confirms the client's side stays silent.

Next

comline-rust maps _return: None → this (notify client method, silent dispatcher arm, plain fn f(&self, …) trait method); _return: Some(KindValue::Unit) stays request/response with an empty ack — finally using KindValue::Unit for its designed purpose (§4.4).

All feature configs green; clippy clean (bar the pre-existing sabi_trait lint).