Add widget for Nushell

[giggio]

Is your feature request related to a problem? Please describe.
Yes, I would like the Navi Widget to work on Nushell.

Describe the solution you'd like
navi widget nushell

Describe alternatives you've considered
Implementing myself. I just did that:
https://github.com/giggio/nuscripts/blob/main/scripts/navi.nu

Additional context
N/A.

[welcome]

Thanks for opening your first issue here! In case you're facing a bug, please update navi to the latest version first. Maybe the bug is already solved! :)

[giggio]

I created an initial implementation, if anyone is interested:
https://github.com/giggio/nuscripts/blob/main/scripts/navi.nu

It needs a little refining, but it is good enough for now.