refactor: Add generic type support to PromisorInterface and Deferred

Author: roxblnfk

src/Deferred.php

@@ -6,6 +6,7 @@
 
 /**
  * @template T
+ * @implements PromisorInterface<T>
  */
 class Deferred implements PromisorInterface
 {

src/PromisorInterface.php

@@ -4,12 +4,15 @@
 
 namespace React\Promise;
 
+/**
+ * @template T
+ */
 interface PromisorInterface
 {
     /**
      * Returns the promise of the deferred.
      *
-     * @return PromiseInterface
+     * @return PromiseInterface<T>
      */
     public function promise();
 }