fix: playback restarting from start of stream

This does a major refactor to using particleId for state of playback
instead of index, since index would change if the particle children data
does partial hydrations and a particle's index changes. Also it
abstracts much of the playback details from the view component.

js/src/lib/firestore-particles.ts

@@ -143,6 +143,10 @@ export function subscribeToParticleChildren(
   return onSnapshot(
     q,
     (snap) => {
+      // onNext(snap.docChanges().map((change) => {
+      //   const data = change.doc.data();
+      //   return { type: change.type, data };
+      // }));
       onData(snap.docs.map((d) => d.data()));
     },
     onError,