Implement QUIC networking for wrsrvd (server) and wrclient (client) using
quinn over rustls with self-signed certificates. Three logical channels:
control (bidirectional), display (server->client unidirectional), and
input (client->server unidirectional).
Server runs tokio in a background thread, communicating with the compositor
via std::sync::mpsc channels. Client exposes an async connect() API that
returns a ServerConnection with methods for sending input and receiving
frames.
Key design note: quinn streams are lazily materialized -- accept_bi/
accept_uni on the peer won't resolve until data is written. The handshake
protocol accounts for this by having each side write immediately after
opening streams.
Message types for control, display, and input channels with serde
derives. Length-prefixed postcard codec with encode/decode/framing.
Seven round-trip tests covering all message types and edge cases.
