Add single-writer invariant comment for fetch position fields

Document why nextFetchChunkIndex and nextFetchRowOffset are safe as
separate AtomicLongs (single prefetch thread writer) unlike
StreamingChunkProvider which needs a bundled FetchPosition holder.

Signed-off-by: Gopal Lal <gopal.lal@databricks.com>

Co-authored-by: Isaac
Signed-off-by: Gopal Lal <gopal.lal@databricks.com>

Author: gopalldb

src/main/java/com/databricks/jdbc/api/impl/arrow/SeaInlineArrowChunkProvider.java

@@ -53,6 +53,10 @@ class SeaInlineArrowChunkProvider implements ChunkProvider {
   // Position tracking
   private final AtomicLong currentChunkIndex = new AtomicLong(-1);
   private final AtomicLong highestFetchedChunkIndex = new AtomicLong(-1);
+  // Single-writer: nextFetchChunkIndex and nextFetchRowOffset are only written by
+  // the prefetch thread (fetchNextChunkInternal), so separate AtomicLongs are safe.
+  // Unlike StreamingChunkProvider where download threads can also update the position
+  // (requiring a bundled FetchPosition holder), this provider has no second writer.
   private final AtomicLong nextFetchChunkIndex = new AtomicLong(1); // 0 is initial chunk
   private final AtomicLong nextFetchRowOffset = new AtomicLong(0);
   private final AtomicLong totalRowCount = new AtomicLong(0);