The following example shows that starting in JDK 23, a HeapByteBuffer and DirectByteBufferR with the same contents are equal according to equals, but have different hashcodes.

I noticed this debugging a test that started failing on JDK 23, and which was putting ByteBuffers in a set and relying on Set#equals.

I haven't verified this yet, but https://bugs.openjdk.org/browse/JDK-8321279 seems like a possible culprit, if the behaviour of the hashCode implementations in Heap-X-Buffer.java.template and X-Buffer.java.template is no longer equivalent.

```java
import static java.nio.charset.StandardCharsets.UTF_8;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Set;

public class X {
  public static void main(String[] args) throws IOException {
    byte[] bytes = "hello world".getBytes(UTF_8);
    Path path = Files.createTempFile("", "");
    Files.write(path, bytes);
    FileChannel chan = FileChannel.open(path, StandardOpenOption.READ);
    MappedByteBuffer one = chan.map(FileChannel.MapMode.READ_ONLY, 0, bytes.length);
    ByteBuffer two = ByteBuffer.wrap(bytes);
    System.err.printf(
        "comparing:\n %s (%s)\n %s (%s)\n", one, one.getClass(), two, two.getClass());
    System.err.printf("equals: %s\n", one.equals(two));
    int oneHash = one.hashCode();
    int twoHash = two.hashCode();
    System.err.printf("hashCode (%d == %d) = %s\n", oneHash, twoHash, oneHash == twoHash);
    System.err.printf("contains: %s\n", Set.of(one).contains(two));
  }
}
```

$ java -fullversion
$ java X.java
openjdk full version "22.0.2+9-70"
comparing:
  java.nio.DirectByteBufferR[pos=0 lim=11 cap=11] (class java.nio.DirectByteBufferR)
  java.nio.HeapByteBuffer[pos=0 lim=11 cap=11] (class java.nio.HeapByteBuffer)
equals: true
hashCode (621715235 == 621715235) = true
contains: true

$ java -fullversion
$ java X.java
openjdk full version "23-ea+34-2361"
comparing:
  java.nio.DirectByteBufferR[pos=0 lim=11 cap=11] (class java.nio.DirectByteBufferR)
  java.nio.HeapByteBuffer[pos=0 lim=11 cap=11] (class java.nio.HeapByteBuffer)
equals: true
hashCode (621715235 == 1923188771) = false