add precise return types to Error#get() and Success#get()

Author: someniatko

src/Error.php

@@ -37,6 +37,7 @@ public function chain(callable $map): ResultInterface
         return $this;
     }
 
+    /** @return TError */
     public function get()
     {
         return $this->value;

src/Success.php

@@ -36,6 +36,7 @@ public function chain(callable $map): ResultInterface
         return $map($this->value);
     }
 
+    /** @return TSuccess */
     public function get()
     {
         return $this->value;