chore: Use more lambda style in stream module.

stream/src/main/scala/org/apache/pekko/stream/impl/LazySource.scala

@@ -74,11 +74,7 @@ import pekko.stream.stage._
             }
           })
 
-        subSink.setHandler(new InHandler {
-          override def onPush(): Unit = {
-            push(out, subSink.grab())
-          }
-        })
+        subSink.setHandler(() => push(out, subSink.grab()))
 
         try {
           val matVal = subFusingMaterializer.materialize(source.toMat(subSink.sink)(Keep.left), inheritedAttributes)

stream/src/main/scala/org/apache/pekko/stream/impl/fusing/ActorGraphInterpreter.scala

@@ -666,10 +666,7 @@ import org.reactivestreams.Subscription
         else {
           waitingForShutdown = true
           val subscriptionTimeout = attributes.mandatoryAttribute[ActorAttributes.StreamSubscriptionTimeout].timeout
-          mat.scheduleOnce(subscriptionTimeout,
-            new Runnable {
-              override def run(): Unit = self ! Abort(GraphInterpreterShell.this)
-            })
+          mat.scheduleOnce(subscriptionTimeout, () => self ! Abort(GraphInterpreterShell.this))
         }
       } else if (interpreter.isSuspended && !resumeScheduled) sendResume(!usingShellLimit)
 

stream/src/main/scala/org/apache/pekko/stream/impl/fusing/StreamOfStreams.scala

@@ -199,9 +199,7 @@ import pekko.util.ccompat.JavaConverters._
         setKeepGoing(false)
         cancelTimer(SubscriptionTimer)
         pull(in)
-        tailSource.setHandler(new OutHandler {
-          override def onPull(): Unit = pull(in)
-        })
+        tailSource.setHandler(() => pull(in))
       }
     }
 

stream/src/main/scala/org/apache/pekko/stream/javadsl/DelayStrategy.scala

@@ -45,9 +45,7 @@ object DelayStrategy {
    * Fixed delay strategy, always returns constant delay for any element.
    * @param delay value of the delay
    */
-  def fixedDelay[T](delay: java.time.Duration): DelayStrategy[T] = new DelayStrategy[T] {
-    override def nextDelay(elem: T): java.time.Duration = delay
-  }
+  def fixedDelay[T](delay: java.time.Duration): DelayStrategy[T] = (_: T) => delay
 
   /**
    * Strategy with linear increasing delay.

stream/src/main/scala/org/apache/pekko/stream/javadsl/Graph.scala

@@ -477,8 +477,7 @@ object Zip {
   def create[A, B]: Graph[FanInShape2[A, B, A Pair B], NotUsed] =
     ZipWith.create(_toPair.asInstanceOf[Function2[A, B, A Pair B]])
 
-  private[this] final val _toPair: Function2[Any, Any, Any Pair Any] =
-    new Function2[Any, Any, Any Pair Any] { override def apply(a: Any, b: Any): Any Pair Any = new Pair(a, b) }
+  private[this] final val _toPair: Function2[Any, Any, Any Pair Any] = (a: Any, b: Any) => new Pair(a, b)
 }
 
 /**
@@ -506,8 +505,7 @@ object ZipLatest {
   def create[A, B]: Graph[FanInShape2[A, B, A Pair B], NotUsed] =
     ZipLatestWith.create(_toPair.asInstanceOf[Function2[A, B, A Pair B]])
 
-  private[this] final val _toPair: Function2[Any, Any, Any Pair Any] =
-    new Function2[Any, Any, Any Pair Any] { override def apply(a: Any, b: Any): Any Pair Any = new Pair(a, b) }
+  private[this] final val _toPair: Function2[Any, Any, Any Pair Any] = (a: Any, b: Any) => new Pair(a, b)
 }
 
 /**

stream/src/main/scala/org/apache/pekko/stream/scaladsl/DelayStrategy.scala

@@ -36,9 +36,7 @@ object DelayStrategy {
    * Fixed delay strategy, always returns constant delay for any element.
    * @param delay value of the delay
    */
-  def fixedDelay(delay: FiniteDuration): DelayStrategy[Any] = new DelayStrategy[Any] {
-    override def nextDelay(elem: Any): FiniteDuration = delay
-  }
+  def fixedDelay(delay: FiniteDuration): DelayStrategy[Any] = (_: Any) => delay
 
   /**
    * Strategy with linear increasing delay.