- Refactor code to use idiomatic Kotlin functions like isNullOrEmpty(), associateBy, and appendRange

- Increase `DiffUtil` threshold in `CursorRecyclerAdapter` to 500 and optimize equality checks
- Simplify locale configuration by removing legacy Android SDK version checks
- Remove unnecessary `@SuppressLint` annotations and `@Volatile` modifiers
- Improve performance of collection operations in `ProductFragment` and `Preferences` using `associateBy` and `firstOrNull`
- Suppress deprecation warnings for `getOpacity` in `DrawableWrapper` and `TabsFragment`
- Clean up service binding logic in `Connection.kt` with better type casting

src/main/kotlin/com/michatec/store/index/IndexHandler.kt

@@ -260,6 +260,6 @@ class IndexHandler(private val repositoryId: Long, private val callback: Callbac
 
   override fun characters(ch: CharArray, start: Int, length: Int) {
     super.characters(ch, start, length)
-    contentBuilder.append(ch, start, length)
+    contentBuilder.appendRange(ch, start, start + length)
   }
 }