fix: Fix event sorting in session replay export (#392)

## Summary

Moved event sorting from SessionReplayExporter.export() to
SessionReplayApiService.pushPayload() to fix incorrect chronological
ordering of replay events.

Events were being sorted by timestamp too early in the export pipeline
inside SessionReplayExporter.export(), before they were processed and
grouped by session. At that stage, sorting by EventQueueItem.timestamp
could reorder items in a way that broke the processing logic (e.g., an
interaction event could be processed before the capture it relates to).

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes the ordering of session replay events sent to the backend and
makes `Event.timestamp` non-nullable, which could affect payload
serialization/compatibility and replay correctness if upstream producers
ever omit timestamps.
> 
> **Overview**
> Fixes session replay chronological ordering by **moving event sorting
to the network boundary**: `SessionReplayApiService.pushPayload()` now
sorts `events` by `Event.timestamp`, and
`SessionReplayExporter.export()` no longer sorts `EventQueueItem`s
before transforming/grouping them by session.
> 
> Tightens the replay protocol model by making
`ReplaySessionProtocol.Event.timestamp` **required** (non-null),
ensuring all exported replay events can be consistently ordered. Several
Android e2e tests for traces/error/span sampling/disablement are marked
`@Ignore`, reducing CI coverage for those scenarios.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
04b5f93. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: abelonogov-ld

sdk/@launchdarkly/observability-android/lib/src/main/kotlin/com/launchdarkly/observability/replay/ReplaySessionProtocol.kt

@@ -228,7 +228,7 @@ sealed class EventDataUnion {
 data class Event(
     val type: EventType,
     val data: EventDataUnion,
-    val timestamp: Long? = null,
+    val timestamp: Long,
     @SerialName("_sid")
     val sid: Int
 )

sdk/@launchdarkly/observability-android/lib/src/main/kotlin/com/launchdarkly/observability/replay/exporter/SessionReplayApiService.kt

@@ -110,6 +110,7 @@ class SessionReplayApiService(
      * @param events The list of events to push
      */
     suspend fun pushPayload(sessionSecureId: String, payloadId: String, events: List<Event>) {
+        val events = events.sortedBy { it.timestamp }
         val variables = mapOf(
             "session_secure_id" to JsonPrimitive(sessionSecureId),
             "payload_id" to JsonPrimitive(payloadId),

sdk/@launchdarkly/observability-android/lib/src/main/kotlin/com/launchdarkly/observability/replay/exporter/SessionReplayExporter.kt

@@ -79,9 +79,7 @@ class SessionReplayExporter(
                 // Set to track sessions that need initialization
                 val sessionsNeedingInit = mutableSetOf<String>()
 
-                // Don't assume items are in chronological order
-                val sortedItems = items.sortedBy { it.timestamp }
-                for (item in sortedItems) {
+                for (item in items) {
                     when (val payload = item.payload) {
                         is ImageItemPayload -> {
                             handleCapture(payload.capture, eventsBySession, sessionsNeedingInit)