Sort events upon creation, and keep ordered (#411)

* Sort events at start, as otherwise we risk misidentifying the last event

* Keep inserted events in the correct order, ensuring we don't misidentify the last event

 - e.g. network conditions mean that 'live' events come in non-sequentially
 - or so that adding custom events to an existing event works

* Ensure we maintain original ordering while inserting a new event which has an identical timestamp to an existing event. This came up with a series of mutations which had the same timestamp but needed to be applied in the correct order

* Fast track the common case of a new event being added which occurs after all prior events

src/replay/index.ts

@@ -129,6 +129,8 @@ export class Replayer {
     events: Array<eventWithTime | string>,
     config?: Partial<playerConfig>,
   ) {
+    events.sort((a1, a2) => a1.timestamp - a2.timestamp);
+
     if (!config?.liveMode && events.length < 2) {
       throw new Error('Replayer need at least 2 events.');
     }
@@ -520,6 +522,8 @@ export class Replayer {
         castFn();
       }
       this.service.send({ type: 'CAST_EVENT', payload: { event } });
+
+      // events are kept sorted by timestamp, check if this is the last event
       if (
         event ===
         this.service.state.context.events[