Mark all classes as final

Classes should be used via composition rather than extension.
This reduces our API footprint and avoids future BC breaks by avoiding
exposing its internal assumptions.

Author: clue

src/CompositeStream.php

@@ -4,7 +4,7 @@
 
 use Evenement\EventEmitter;
 
-class CompositeStream extends EventEmitter implements DuplexStreamInterface
+final class CompositeStream extends EventEmitter implements DuplexStreamInterface
 {
     protected $readable;
     protected $writable;

src/DuplexResourceStream.php

@@ -6,7 +6,7 @@
 use React\EventLoop\LoopInterface;
 use InvalidArgumentException;
 
-class DuplexResourceStream extends EventEmitter implements DuplexStreamInterface
+final class DuplexResourceStream extends EventEmitter implements DuplexStreamInterface
 {
     private $stream;
     private $loop;

src/ReadableResourceStream.php

@@ -6,7 +6,7 @@
 use React\EventLoop\LoopInterface;
 use InvalidArgumentException;
 
-class ReadableResourceStream extends EventEmitter implements ReadableStreamInterface
+final class ReadableResourceStream extends EventEmitter implements ReadableStreamInterface
 {
     /**
      * @var resource

src/ThroughStream.php

@@ -73,7 +73,7 @@
  * @see DuplexStreamInterface::close()
  * @see WritableStreamInterface::pipe()
  */
-class ThroughStream extends EventEmitter implements DuplexStreamInterface
+final class ThroughStream extends EventEmitter implements DuplexStreamInterface
 {
     private $readable = true;
     private $writable = true;

src/Util.php

@@ -2,7 +2,7 @@
 
 namespace React\Stream;
 
-class Util
+final class Util
 {
     /**
      * Pipes all the data from the given $source into the $dest

src/WritableResourceStream.php

@@ -5,7 +5,7 @@
 use Evenement\EventEmitter;
 use React\EventLoop\LoopInterface;
 
-class WritableResourceStream extends EventEmitter implements WritableStreamInterface
+final class WritableResourceStream extends EventEmitter implements WritableStreamInterface
 {
     private $stream;
     private $loop;