debug: add getPos() method to track position queries

Added getPos() to SeaweedOutputStream to understand when and how
Hadoop/Parquet queries the output stream position.

Current mystery:
- Files are written correctly (totalBytesWritten=position=chunks)
- But Parquet expects 78 more bytes when reading
- year=2020: wrote 696, expects 774 (missing 78)
- year=2021: wrote 684, expects 762 (missing 78)

The consistent 78-byte discrepancy suggests either:
A) Parquet calculates row group size before finalizing footer
B) FSDataOutputStream tracks position differently than our stream
C) Footer is written with stale/incorrect metadata
D) File size is cached/stale during rename operation

getPos() logging will show if Parquet/Hadoop queries position
and what value is returned vs what was actually written.

other/java/client/src/main/java/seaweedfs/client/SeaweedOutputStream.java

@@ -34,7 +34,7 @@ public class SeaweedOutputStream extends OutputStream {
     private long outputIndex;
     private String replication = "";
     private String collection = "";
-    private long totalBytesWritten = 0;  // Track total bytes for debugging
+    private long totalBytesWritten = 0; // Track total bytes for debugging
 
     public SeaweedOutputStream(FilerClient filerClient, final String fullpath) {
         this(filerClient, fullpath, "");
@@ -90,6 +90,19 @@ public class SeaweedOutputStream extends OutputStream {
         this.collection = collection;
     }
 
+    /**
+     * Get the current position in the output stream.
+     * This returns the total position including both flushed and buffered data.
+     * 
+     * @return current position (flushed + buffered bytes)
+     */
+    public synchronized long getPos() {
+        long currentPos = position + buffer.position();
+        LOG.info("[DEBUG-2024] 📍 getPos() called: flushedPosition={} bufferPosition={} returning={} path={}", 
+                position, buffer.position(), currentPos, path);
+        return currentPos;
+    }
+
     public static String getParentDirectory(String path) {
         int protoIndex = path.indexOf("://");
         if (protoIndex >= 0) {