GH-3520: Cleanup binary write path

Two small cleanups on the binary write side:

1. DeltaByteArrayWriter: replace v.getBytes() with v.copy().getBytesUnsafe()
   to avoid the unconditional Arrays.copyOf that getBytes() performs for
   ByteArrayBackedBinary. copy() is a no-op for constant Binaries, and
   getBytesUnsafe() returns the backing array directly. For reused-buffer
   Binaries (e.g. ByteBufferBackedBinary over a slab being mutated), copy()
   still snapshots them so correctness is preserved.

2. FixedLenByteArrayPlainValuesWriter: drop the unused LittleEndianDataOutputStream
   wrapper (only used to call Binary.writeTo(), which works directly with
   the underlying CapacityByteArrayOutputStream). The trailing out.flush()
   in getBytes() is also dead. Same pattern as #3517 fixed in
   DeltaLengthByteArrayValuesWriter.

No public API change. No file format change.

Validation: parquet-column 573 tests pass. Built with
-Dspotless.check.skip=true -Drat.skip=true -Djapicmp.skip=true.

Author: iemejia

parquet-column/src/main/java/org/apache/parquet/column/values/deltastrings/DeltaByteArrayWriter.java

@@ -89,7 +89,10 @@ public String memUsageString(String prefix) {
   @Override
   public void writeBytes(Binary v) {
     int i = 0;
-    byte[] vb = v.getBytes();
+    // copy() is a no-op for constant (non-reused) Binaries, and getBytesUnsafe()
+    // returns the backing array directly for ByteArrayBackedBinary — avoiding
+    // the unconditional array copy that getBytes() always performs.
+    byte[] vb = v.copy().getBytesUnsafe();
     int length = previous.length < vb.length ? previous.length : vb.length;
     // find the number of matching prefix bytes between this value and the previous one
     for (i = 0; (i < length) && (previous[i] == vb[i]); i++)

parquet-column/src/main/java/org/apache/parquet/column/values/plain/FixedLenByteArrayPlainValuesWriter.java

@@ -22,7 +22,6 @@
 import org.apache.parquet.bytes.ByteBufferAllocator;
 import org.apache.parquet.bytes.BytesInput;
 import org.apache.parquet.bytes.CapacityByteArrayOutputStream;
-import org.apache.parquet.bytes.LittleEndianDataOutputStream;
 import org.apache.parquet.column.Encoding;
 import org.apache.parquet.column.values.ValuesWriter;
 import org.apache.parquet.io.ParquetEncodingException;
@@ -37,7 +36,6 @@ public class FixedLenByteArrayPlainValuesWriter extends ValuesWriter {
   private static final Logger LOG = LoggerFactory.getLogger(PlainValuesWriter.class);
 
   private CapacityByteArrayOutputStream arrayOut;
-  private LittleEndianDataOutputStream out;
   private int length;
   private ByteBufferAllocator allocator;
 
@@ -46,7 +44,6 @@ public FixedLenByteArrayPlainValuesWriter(
     this.length = length;
     this.allocator = allocator;
     this.arrayOut = new CapacityByteArrayOutputStream(initialSize, pageSize, this.allocator);
-    this.out = new LittleEndianDataOutputStream(arrayOut);
   }
 
   @Override
@@ -56,7 +53,7 @@ public final void writeBytes(Binary v) {
           "Fixed Binary size " + v.length() + " does not match field type length " + length);
     }
     try {
-      v.writeTo(out);
+      v.writeTo(arrayOut);
     } catch (IOException e) {
       throw new ParquetEncodingException("could not write fixed bytes", e);
     }
@@ -69,11 +66,6 @@ public long getBufferedSize() {
 
   @Override
   public BytesInput getBytes() {
-    try {
-      out.flush();
-    } catch (IOException e) {
-      throw new ParquetEncodingException("could not write page", e);
-    }
     LOG.debug("writing a buffer of size {}", arrayOut.size());
     return BytesInput.from(arrayOut);
   }