Add batch read methods to PlainValuesReader with bulk ByteBuffer view reads

Add readIntegers/readFloats/readLongs/readDoubles batch methods to all
PlainValuesReader inner classes. All four types use bulk typed-buffer
view reads (e.g. buffer.asIntBuffer().get(dest, offset, count)) which
bypass per-value bounds checks and position updates.

Benchmark results (PlainDecodingBenchmark, 100K values, pre-allocated arrays):

  Type    Per-value (ops/s)  Batch (ops/s)  Speedup
  INT32        5,454M          28,256M       +418%
  FLOAT        5,407M          25,798M       +377%
  INT64        5,408M           8,088M        +50%
  DOUBLE       7,404M           7,965M         +8%

Author: iemejia

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

@@ -67,6 +67,15 @@ public void skip(int n) {
     public double readDouble() {
       return buffer.getDouble();
     }
+
+    /**
+     * Reads {@code count} doubles into {@code dest} starting at {@code offset}.
+     * Uses a bulk {@link java.nio.DoubleBuffer} view read for reduced per-value overhead.
+     */
+    public void readDoubles(double[] dest, int offset, int count) {
+      buffer.asDoubleBuffer().get(dest, offset, count);
+      buffer.position(buffer.position() + count * Double.BYTES);
+    }
   }
 
   public static class FloatPlainValuesReader extends PlainValuesReader {
@@ -80,6 +89,15 @@ public void skip(int n) {
     public float readFloat() {
       return buffer.getFloat();
     }
+
+    /**
+     * Reads {@code count} floats into {@code dest} starting at {@code offset}.
+     * Uses a bulk {@link java.nio.FloatBuffer} view read for reduced per-value overhead.
+     */
+    public void readFloats(float[] dest, int offset, int count) {
+      buffer.asFloatBuffer().get(dest, offset, count);
+      buffer.position(buffer.position() + count * Float.BYTES);
+    }
   }
 
   public static class IntegerPlainValuesReader extends PlainValuesReader {
@@ -93,6 +111,15 @@ public void skip(int n) {
     public int readInteger() {
       return buffer.getInt();
     }
+
+    /**
+     * Reads {@code count} integers into {@code dest} starting at {@code offset}.
+     * Uses a bulk {@link java.nio.IntBuffer} view read for reduced per-value overhead.
+     */
+    public void readIntegers(int[] dest, int offset, int count) {
+      buffer.asIntBuffer().get(dest, offset, count);
+      buffer.position(buffer.position() + count * Integer.BYTES);
+    }
   }
 
   public static class LongPlainValuesReader extends PlainValuesReader {
@@ -106,5 +133,14 @@ public void skip(int n) {
     public long readLong() {
       return buffer.getLong();
     }
+
+    /**
+     * Reads {@code count} longs into {@code dest} starting at {@code offset}.
+     * Uses a bulk {@link java.nio.LongBuffer} view read for reduced per-value overhead.
+     */
+    public void readLongs(long[] dest, int offset, int count) {
+      buffer.asLongBuffer().get(dest, offset, count);
+      buffer.position(buffer.position() + count * Long.BYTES);
+    }
   }
 }