fix: use targetChunkSize for chunk move distance in chunkByCharacters

Author: hyochan

packages/android/locanara/src/main/kotlin/com/locanara/rag/DocumentChunker.kt

@@ -218,7 +218,7 @@ class DocumentChunker(
             }
 
             // Move forward with overlap
-            val moveDistance = maxOf(1, chunkSize - config.chunkOverlap)
+            val moveDistance = maxOf(1, config.targetChunkSize - config.chunkOverlap)
             currentIndex += moveDistance
         }