message: refactor(useViewport): use shallow for selector
diff: +import shallow from 'zustand/shallow';
  +
  import { useStore } from '../store';
  import { Viewport, ReactFlowState } from '../types';
  @@ -8,7 +10,7 @@ const viewportSelector = (state: ReactFlowState) => ({
  });
  function useViewport(): Viewport {
  - const viewport = useStore(viewportSelector);
  + const viewport = useStore(viewportSelector, shallow);
  return viewport;
  }
  