feat(napi): implement serve() function with WraithServer, WraithServerStream, and ConnectionInfo

Expose NAPI serve() per ADR-016. WraithServer provides close() and
onConnection(callback) for receiving SSH channel streams from
incoming connections. Each connection produces a WraithServerStream
(Duplex-like read/write/close) with ConnectionInfo (remoteAddr,
transportKind). Supports TCP transport with optional authorizedKeys
and certAuthority auth. TLS and iroh transports return helpful errors
indicating future support.

Cargo.lock

@@ -5636,6 +5636,7 @@ dependencies = [
 name = "wraith-napi"
 version = "0.1.0"
 dependencies = [
+ "async-trait",
  "napi",
  "napi-derive",
  "russh",