chore: Add PekkoManagedBlocker to reduce memory.

actor/src/main/scala/org/apache/pekko/dispatch/ThreadPoolBuilder.scala

@@ -173,19 +173,23 @@ object MonitorableThreadFactory {
   val doNothing: Thread.UncaughtExceptionHandler =
     new Thread.UncaughtExceptionHandler() { def uncaughtException(thread: Thread, cause: Throwable) = () }
 
+  private class PekkoManagedBlocker[T](thunk: => T)
+      extends AtomicReference[Option[T]](None) with ForkJoinPool.ManagedBlocker {
+    final override def block(): Boolean = {
+      set(Some(thunk))
+      true
+    }
+
+    final override def isReleasable: Boolean = get().isDefined // Exception intended if None
+  }
+
   private[pekko] class PekkoForkJoinWorkerThread(_pool: ForkJoinPool)
       extends ForkJoinWorkerThread(_pool)
       with BlockContext {
-    override def blockOn[T](thunk: => T)(implicit permission: CanAwait): T = {
-      val result = new AtomicReference[Option[T]](None)
-      ForkJoinPool.managedBlock(new ForkJoinPool.ManagedBlocker {
-        def block(): Boolean = {
-          result.set(Some(thunk))
-          true
-        }
-        def isReleasable = result.get.isDefined
-      })
-      result.get.get // Exception intended if None
+    final override def blockOn[T](thunk: => T)(implicit permission: CanAwait): T = {
+      val blocker = new PekkoManagedBlocker(thunk)
+      ForkJoinPool.managedBlock(blocker)
+      blocker.get.get // Exception intended if None
     }
   }
 }