fix: Override FSDataOutputStream.getPos() to use SeaweedOutputStream position

CRITICAL FIX for Parquet 78-byte EOF error!

Root Cause Analysis:
- Hadoop's FSDataOutputStream tracks position with an internal counter
- It does NOT call SeaweedOutputStream.getPos() by default
- When Parquet writes data and calls getPos() to record column chunk offsets,
  it gets FSDataOutputStream's counter, not SeaweedOutputStream's actual position
- This creates a 78-byte mismatch between recorded offsets and actual file size
- Result: EOFException when reading (tries to read beyond file end)

The Fix:
- Override getPos() in the anonymous FSDataOutputStream subclass
- Delegate to SeaweedOutputStream.getPos() which returns 'position + buffer.position()'
- This ensures Parquet gets the correct position when recording metadata
- Column chunk offsets in footer will now match actual data positions

This should fix the consistent 78-byte discrepancy we've been seeing across
all Parquet file writes (regardless of file size: 684, 693, 1275 bytes, etc.)

other/java/hdfs3/src/main/java/seaweed/hdfs/SeaweedFileSystem.java

@@ -13,7 +13,6 @@ import seaweedfs.client.FilerProto;
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
-import java.io.OutputStream;
 import java.net.URI;
 import java.util.EnumSet;
 import java.util.List;
@@ -112,9 +111,16 @@ public class SeaweedFileSystem extends FileSystem {
                 replicaPlacement = String.format("%03d", replication - 1);
             }
             int seaweedBufferSize = this.getConf().getInt(FS_SEAWEED_BUFFER_SIZE, FS_SEAWEED_DEFAULT_BUFFER_SIZE);
-            OutputStream outputStream = seaweedFileSystemStore.createFile(path, overwrite, permission,
+            SeaweedHadoopOutputStream outputStream = (SeaweedHadoopOutputStream) seaweedFileSystemStore.createFile(path, overwrite, permission,
                     seaweedBufferSize, replicaPlacement);
-            return new FSDataOutputStream(outputStream, statistics);
+            // Use custom FSDataOutputStream that delegates getPos() to our stream
+            return new FSDataOutputStream(outputStream, statistics) {
+                @Override
+                public long getPos() {
+                    // Delegate to SeaweedOutputStream's position tracking
+                    return outputStream.getPos();
+                }
+            };
         } catch (Exception ex) {
             LOG.error("Failed to create file: {} bufferSize:{} blockSize:{}", path, bufferSize, blockSize, ex);
             throw new IOException("Failed to create file: " + path, ex);
@@ -156,8 +162,15 @@ public class SeaweedFileSystem extends FileSystem {
         path = qualify(path);
         try {
             int seaweedBufferSize = this.getConf().getInt(FS_SEAWEED_BUFFER_SIZE, FS_SEAWEED_DEFAULT_BUFFER_SIZE);
-            OutputStream outputStream = seaweedFileSystemStore.createFile(path, false, null, seaweedBufferSize, "");
-            return new FSDataOutputStream(outputStream, statistics);
+            SeaweedHadoopOutputStream outputStream = (SeaweedHadoopOutputStream) seaweedFileSystemStore.createFile(path, false, null, seaweedBufferSize, "");
+            // Use custom FSDataOutputStream that delegates getPos() to our stream
+            return new FSDataOutputStream(outputStream, statistics) {
+                @Override
+                public long getPos() {
+                    // Delegate to SeaweedOutputStream's position tracking
+                    return outputStream.getPos();
+                }
+            };
         } catch (Exception ex) {
             LOG.error("Failed to append to file: {} bufferSize:{}", path, bufferSize, ex);
             throw new IOException("Failed to append to file: " + path, ex);