Group livekitRoomItems$ by connection

The old reducer keyed items by service URL and mutated the accumulator's
entries in place, so a transport without a service URL could not be
represented and items were not safe to compare. Group members by their
Connection object instead and carry the whole transport on the item, which
the audio renderer now receives in place of a URL.

sdk/main.ts

@@ -231,7 +231,7 @@ export async function createMatrixRTCSdk(
       complete: () => {
         logger.info("Livekit room items subscription completed");
         for (const item of callViewModel.livekitRoomItems$.value) {
-          logger.info("unregistering room item from room", item.url);
+          logger.info("unregistering room item from room", item.transport);
           item.livekitRoom.unregisterTextStreamHandler(TEXT_LK_TOPIC);
         }
       },