fix: use multiplatform hex padding in room state tests

String.format is JVM-only and broke the iOS Klib compile of commonTest.
Replace "%064x".format(...) with toString(16).padStart(64, '0').

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/RoomReactionsStateTest.kt

@@ -37,7 +37,7 @@ class RoomReactionsStateTest {
         to: String?,
         content: String,
         createdAt: Long,
-        id: String = "%064x".format(nextEventId++),
+        id: String = (nextEventId++).toString(16).padStart(64, '0'),
     ): ReactionEvent {
         val tags =
             buildList<Array<String>> {

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/RoomZapsStateTest.kt

@@ -45,7 +45,7 @@ class RoomZapsStateTest {
         from: String,
         to: String?,
         createdAt: Long,
-        id: String = "%064x".format(nextEventId++),
+        id: String = (nextEventId++).toString(16).padStart(64, '0'),
     ): LnZapEvent {
         val tags =
             buildList<Array<String>> {