aimdb-tcp-connector — TCP transport (tokio + embassy-net)

[lxsaah]

Follow-up to #39 / doc 041. Its own PR, built on the merged Phase 6 foundation (generic SessionClientConnector/SessionServerConnector, no_std AimxCodec, the aimdb-uds-connector template).

First real new transport (UDS was only relocated) — proves the "transport = thin crate" model holds.

Scope

• New crate aimdb-tcp-connector, modeled on aimdb-uds-connector + the dual-module pattern of aimdb-mqtt-connector (tokio-runtime / embassy-runtime features).
• Transport triple: TcpConnection (newline- or length-prefix framing), TcpDialer, TcpListener.
• Sugar: TcpClient (= SessionClientConnector<TcpDialer, AimxCodec>), TcpServer (= SessionServerConnector<...> + AimxDispatch).
• tokio half (tokio::net::TcpStream/TcpListener) — std.
• Embassy half (embassy-net) — client + cross-compile only; the Embassy server half waits on no_std AimX server (dispatch) port — cross-cutting AnyRecord + RecordMetadataTracker de-std #120 (needs no_std AimxDispatch).
• URL form tcp://host:port (parse via existing ConnectorUrl or a small parser).

Verification

• AimDb <-> AimDb over TCP loopback round-trip test (mirror aimdb-websocket-connector's ws_roundtrip/e2e).
• make test-embedded: cargo check -p aimdb-tcp-connector --target thumbv7em-none-eabihf --features embassy-runtime.
• Wire into Makefile build/test/clippy/test-embedded.

Notes

• embassy-net is already a workspace dependency.
• Framing lives in TcpConnection; AimxCodec is reused unchanged.