=str - Various internal Akka Stream improvements

* Gives Inlets and Outlets a `carbonCopy` method and switches to allocate them via `apply`
* Removes 4 Array allocations per FanIn and uses a bitmasked array instead
* Makes the FlattenStrategy.concat instance a singleton

akka-http-core/src/main/scala/akka/http/impl/engine/client/PoolConductor.scala

@@ -28,9 +28,9 @@ private object PoolConductor {
 
     override def deepCopy(): Shape =
       Ports(
-        new Inlet(requestIn.toString),
-        new Inlet(slotEventIn.toString),
-        slotOuts.map(o ⇒ new Outlet(o.toString)))
+        requestIn.carbonCopy(),
+        slotEventIn.carbonCopy(),
+        slotOuts.map(_.carbonCopy()))
 
     override def copyFromPorts(inlets: immutable.Seq[Inlet[_]], outlets: immutable.Seq[Outlet[_]]): Shape =
       Ports(

akka-http-core/src/main/scala/akka/http/impl/engine/ws/MessageToFrameRenderer.scala

@@ -32,6 +32,6 @@ private[http] object MessageToFrameRenderer {
         case bm: BinaryMessage          ⇒ streamedFrames(Opcode.Binary, bm.dataStream)
         case TextMessage.Strict(text)   ⇒ strictFrames(Opcode.Text, ByteString(text, "UTF-8"))
         case tm: TextMessage            ⇒ streamedFrames(Opcode.Text, tm.textStream.transform(() ⇒ new Utf8Encoder))
-      }.flatten(FlattenStrategy.Concat())
+      }.flatten(FlattenStrategy.concat)
   }
 }

akka-http-core/src/main/scala/akka/http/impl/util/StreamUtils.scala

@@ -218,9 +218,9 @@ private[http] object StreamUtils {
   }
 
   def oneTimePublisherSink[In](cell: OneTimeWriteCell[Publisher[In]], name: String): Sink[In, Publisher[In]] =
-    new Sink[In, Publisher[In]](new OneTimePublisherSink(none, SinkShape(new Inlet(name)), cell))
+    new Sink[In, Publisher[In]](new OneTimePublisherSink(none, SinkShape(Inlet(name)), cell))
   def oneTimeSubscriberSource[Out](cell: OneTimeWriteCell[Subscriber[Out]], name: String): Source[Out, Subscriber[Out]] =
-    new Source[Out, Subscriber[Out]](new OneTimeSubscriberSource(none, SourceShape(new Outlet(name)), cell))
+    new Source[Out, Subscriber[Out]](new OneTimeSubscriberSource(none, SourceShape(Outlet(name)), cell))
 
   /** A copy of PublisherSink that allows access to the publisher through the cell but can only materialized once */
   private class OneTimePublisherSink[In](attributes: Attributes, shape: SinkShape[In], cell: OneTimeWriteCell[Publisher[In]])