expose when data was last received from the websocket client

[bentsku]

Motivation

A server that implements an idle timeout has to know when the client was last active. The listener can track the messages it receives, but not the control frames: the twisted channel answers pings itself on the reactor thread, so a client that keeps its connection alive with pings looks idle to the listener.

Changes

• WebSocketAdapter.last_received_at and WebSocket.last_received_at: the time.monotonic() time at which data was last received from the client, or at which the connection was created if nothing was received yet.
• twisted: WebSocketChannel updates it on every dataReceived, so pings, pongs and partial frames count too.
• ASGI: updated when the listener receives a message. ASGI servers don't pass control frames on to the application, so pings can't count there.

Testing

• New test_last_received_at_message (twisted and asgi): the timestamp after receiving a message must be later than the time the client sent it.
• New test_last_received_at_ping (twisted): a ping alone must move the timestamp forward.
• Both twisted tests fail when dataReceived doesn't update the timestamp. The full suite passes (195 tests) and lint is clean.

🤖 Generated with Claude Code