Mark all connector 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/Connector.php

@@ -15,7 +15,7 @@
  * @see DnsConnector for the newer replacement
  * @see ConnectorInterface for the base interface
  */
-class Connector implements ConnectorInterface
+final class Connector implements ConnectorInterface
 {
     private $connector;
 

src/DnsConnector.php

@@ -3,11 +3,10 @@
 namespace React\SocketClient;
 
 use React\Dns\Resolver\Resolver;
-use React\Stream\Stream;
 use React\Promise;
 use React\Promise\CancellablePromiseInterface;
 
-class DnsConnector implements ConnectorInterface
+final class DnsConnector implements ConnectorInterface
 {
     private $connector;
     private $resolver;

src/SecureConnector.php

@@ -5,9 +5,8 @@
 use React\EventLoop\LoopInterface;
 use React\Stream\Stream;
 use React\Promise;
-use React\Promise\CancellablePromiseInterface;
 
-class SecureConnector implements ConnectorInterface
+final class SecureConnector implements ConnectorInterface
 {
     private $connector;
     private $streamEncryption;

src/TcpConnector.php

@@ -3,12 +3,10 @@
 namespace React\SocketClient;
 
 use React\EventLoop\LoopInterface;
-use React\Dns\Resolver\Resolver;
 use React\Stream\Stream;
 use React\Promise;
-use React\Promise\Deferred;
 
-class TcpConnector implements ConnectorInterface
+final class TcpConnector implements ConnectorInterface
 {
     private $loop;
     private $context;

src/TimeoutConnector.php

@@ -5,11 +5,8 @@
 use React\SocketClient\ConnectorInterface;
 use React\EventLoop\LoopInterface;
 use React\Promise\Timer;
-use React\Stream\Stream;
-use React\Promise\Promise;
-use React\Promise\CancellablePromiseInterface;
 
-class TimeoutConnector implements ConnectorInterface
+final class TimeoutConnector implements ConnectorInterface
 {
     private $connector;
     private $timeout;

src/UnixConnector.php

@@ -14,7 +14,7 @@
  * Unix domain sockets use atomic operations, so we can as well emulate
  * async behavior.
  */
-class UnixConnector implements ConnectorInterface
+final class UnixConnector implements ConnectorInterface
 {
     private $loop;