A WebSocket and SSE API shared by WO and ng #90

WO apps get WebSockets and SSE from wo-adaptor-jetty-push (about 1,000 lines). ng should offer the same API so push code moves between the frameworks unchanged: one framework-neutral library both can use, with a thin shim on each side.

The neutral core (no framework dependency)

• WebSocket session: send text or binary, close, attributes, remote address. WOWebSocketSession is already neutral apart from its name.
• Handler: an interface with default no-op methods (onConnect, onTextMessage, onBinaryMessage, onClose, onError). It replaces the abstract WOWebSocketHandler.
  • application() isn't needed; both frameworks have a static one.
  • Heartbeat becomes a small utility instead of an executor in the base class.
• Handshake: a small record (path, query, headers, cookies, remote address) passed to onConnect instead of a framework request.
• SSE: SSEStream (event formatting, keep-alive, the blocking stream) and SSEHub. Both are neutral except SSEStream.response().
• No registration mechanism: each framework maps endpoints its own way.

Both adaptors are on Jetty 12.1.13, so the Jetty WebSocket glue (listener, session wrapper) can be shared too.

WO shim (in wo-adaptor-jetty-push)

• Keeps WOWebSocketRegistry, the upgrade wiring through JettyHandlerDecorator, and a handler variant that receives the WORequest.
• An SSEStream → WOResponse adapter.
• Keeps today's com.webobjects.appserver.* names as thin wrappers so existing apps don't break. Related: Pick a package name instead of com.webobjects undur/wo-adaptor-jetty#3 (package name), WebSocket support: smaller items left over from #13 undur/wo-adaptor-jetty#16 (leftover WebSocket items).

ng shim

• WebSocket endpoints are routes: mapped in routes(), with the upgrade wired in ng-adaptor-jetty.
• The handshake offers the request and its context, so context.session() ties a socket to a session.
• An SSEStream → NGResponse adapter. It needs lengthless streaming responses (Streaming responses without a known length #89).
• Remove the experimental Jakarta WebSocket support in ng-adaptor-jetty-servlet (NGWebSocketEndpoint) in favour of this.