fix: Prevent multiple callbacks

After a callback is performed, the executor address transient storage is set to 0 so that multiple callbacks can't be performed for the same swap

--- don't change below this line ---
ENG-4411 Took 22 minutes

foundry/src/Dispatcher.sol

@@ -109,5 +109,10 @@ contract Dispatcher {
                 )
             );
         }
+
+        // to prevent multiple callbacks
+        assembly {
+            tstore(0, 0)
+        }
     }
 }