use createSomething$ mathods instead of classes

Rename several classes/behaviors to factory-style creators and adapt
call wiring and tests accordingly:
- Replace ConnectionManager class with createConnectionManager$ which
  returns transports$, connectionManagerData$, connections$
- Convert MatrixLivekitMerger to createMatrixLivekitMembers$
  (matrixLivekitMerger$)
- Rename sessionBehaviors$, localMembership$, localTransport$ to
  createSessionMembershipsAndTransports$, createLocalMembership$,
  createLocalTransport$
- Adjust participant types and hook up connectOptions$; expose join via
  localMembership.requestConnect
- Update tests to use the new factory APIs

src/state/remoteMembers/integration.test.ts

@@ -18,7 +18,7 @@ import { ECConnectionFactory } from "./ConnectionFactory.ts";
 import { type OpenIDClientParts } from "../../livekit/openIDSFU.ts";
 import { mockMediaDevices, withTestScheduler } from "../../utils/test";
 import { type ProcessorState } from "../../livekit/TrackProcessorContext.tsx";
-import { MatrixLivekitMerger } from "./matrixLivekitMerger.ts";
+import { matrixLivekitMerger$ } from "./matrixLivekitMerger.ts";
 import type { CallMembership, Transport } from "matrix-js-sdk/lib/matrixrtc";
 import { TRANSPORT_1 } from "./ConnectionManager.test.ts";
 
@@ -39,9 +39,9 @@ let connectionManager: ConnectionManager;
 
 function createLkMerger(
   memberships$: Observable<CallMembership[]>,
-): MatrixLivekitMerger {
+): matrixLivekitMerger$ {
   const mockRoomEmitter = new EventEmitter();
-  return new MatrixLivekitMerger(
+  return new matrixLivekitMerger$(
     testScope,
     memberships$,
     connectionManager,