[paginationStore] Add `onChange` callback

[techniq]

While you can use a changeStore to accomplish the task of calling a function when you change page/etc, being able to provide a paginationStore({ onChange: () => ... }) would simplify this case.

Adding something like...

if (props?.onChange) {
  state.subscribe(props.onChange)
}

...to paginationStore should work.

See discussion