Update checker

[pi0]

A simple fetch to npm registry probably does the trick for MVP.

We might support disk caching for faster responses later.

Optional: #9 for usage

Depends on #5 for banner format

[so1ve]

How about move these additional functions into plugins to keep the citty core as lite as possible? Sometimes user may not want to add these functions to their app.

[pi0]

I already dediced to move cli formating utils and prompt to consola. this might as well be moved to nypm for instance.

[Flowko]

any news about this? would be great to have it built in citty,
saw ur tweet https://twitter.com/_pi0_/status/1709115151633584250