UseLenis() hook withour callback

[robinNavas]

Hi, great work on Lenis-scroll !

I think it would make sense to allow the use of useLenis hook without callback function in order to get only the lenis instance. For example I store it as a variable and call lenis.scrollTo() when some condition are fulfilled.

To be clearer: const lenis = useLenis() instead of const lenis = useLenis(() => {})

Maybe I don't use correctly the feature btw.

[clementroche]

#314