move zoom delta to InputAction.ZOOM for FixedOrbit rotation delegate

thermion_dart/lib/src/input/src/implementations/fixed_orbit_camera_rotation_delegate.dart

@@ -48,12 +48,13 @@ class FixedOrbitRotateInputHandlerDelegate implements InputHandlerDelegate {
         _queuedZoomDelta += delta.z;
         break;
       case InputAction.PICK:
-        // Assuming PICK is used for zoom in this context
-        _queuedZoomDelta += delta.z;
         break;
       case InputAction.NONE:
         // Do nothing
         break;
+      case InputAction.ZOOM:
+        _queuedZoomDelta += delta.z;
+        break;
     }
   }