[SPARK-53128][CORE] Include unmanaged memory bytes in the usage log before execution memory OOM

### What changes were proposed in this pull request?

We have a log before OOM for off-heap memory allocation.

Before the change, the log is:

> 25/08/05 16:44:32 INFO TaskMemoryManager: 100 bytes of memory are used for execution and 100 bytes of memory are used for storage

After:

> 25/08/05 16:44:32 INFO TaskMemoryManager: 100 bytes of memory are used for execution and 100 bytes of memory are used for storage and 500 bytes of memory are used but unmanaged

### Why are the changes needed?

Following #51708, to allow user to know the reason if the unmanaged memory causes OOM.

### Does this PR introduce _any_ user-facing change?

Only changes a log message.

### How was this patch tested?

Existing tests.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #51848 from zhztheplayer/wip-53128.

Authored-by: Hongze Zhang <hongze.zzz123@gmail.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit c4ad381)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: zhztheplayer

core/src/main/java/org/apache/spark/memory/TaskMemoryManager.java

@@ -339,9 +339,12 @@ public void showMemoryUsage() {
         MDC.of(LogKeys.MEMORY_SIZE, memoryNotAccountedFor),
         MDC.of(LogKeys.TASK_ATTEMPT_ID, taskAttemptId));
       logger.info(
-        "{} bytes of memory are used for execution and {} bytes of memory are used for storage",
+        "{} bytes of memory are used for execution " +
+                "and {} bytes of memory are used for storage " +
+                "and {} bytes of unmanaged memory are used",
         MDC.of(LogKeys.EXECUTION_MEMORY_SIZE, memoryManager.executionMemoryUsed()),
-        MDC.of(LogKeys.STORAGE_MEMORY_SIZE,  memoryManager.storageMemoryUsed()));
+        MDC.of(LogKeys.STORAGE_MEMORY_SIZE,  memoryManager.storageMemoryUsed()),
+        MDC.of(LogKeys.MEMORY_SIZE, UnifiedMemoryManager$.MODULE$.getUnmanagedMemoryUsed()));
     }
   }
 

core/src/main/scala/org/apache/spark/memory/UnifiedMemoryManager.scala

@@ -273,6 +273,14 @@ object UnifiedMemoryManager extends Logging {
   // Atomic flag to ensure polling is only started once per JVM
   private val pollingStarted = new AtomicBoolean(false)
 
+  /**
+   * Returns the total unmanaged memory in bytes, including both
+   * on-heap unmanaged memory and off-heap unmanaged memory.
+   */
+  private[spark] def getUnmanagedMemoryUsed: Long = {
+    UnifiedMemoryManager.unmanagedOnHeapUsed.get() + UnifiedMemoryManager.unmanagedOffHeapUsed.get()
+  }
+
   /**
    * Register an unmanaged memory consumer to track its memory usage.
    *