specify deps in useEffect and use useCallback for pushEvent

[vonagam]

To avoid running calling the effect function on every rerender deps need to be specified. Makes sense to mark liveState as one.

To avoid creating new pushEvent function on each rerender (and potentially cause unneeded rerenders if it is used as a prop or as a dep) useCallback can be used.

Specify type of event argument as a string in pushEvent.

Also looking at published filed seems that build folder is missing but there are useLiveState.ts and tsconfig.json. I think it makes sense to add files field to package.json to prevent exposing unnecessary files.