fix(deps): update kotlin to 2.3.0 (#5917)

* fix(deps): update kotlin to 2.3.0

* Cleanup - remove `datetime` compat version

* Fix several lint issues caused by the Kotlin compiler inference working better (checks in nullables, vars, etc.)

* Fix tests by removing mock in `File.readBytes`, it seems like it's no longer allowed. Using a tmp file works well enough.

---------

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Benoit Marty <benoit@matrix.org>
Co-authored-by: Jorge Martín <jorgem@element.io>

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/TimelinePresenter.kt

@@ -394,9 +394,8 @@ class TimelinePresenter(
             newMostRecentItemId != prevMostRecentItemIdValue
 
         if (hasNewEvent) {
-            val newMostRecentEvent = newMostRecentItem
             // Scroll to bottom if the new event is from me, even if sent from another device
-            val fromMe = newMostRecentEvent?.isMine == true
+            val fromMe = newMostRecentItem.isMine
             newEventState.value = if (fromMe) {
                 NewEventState.FromMe
             } else {