Also support data-dir and cache-dir - like nu does

[ddanier]

Is your feature request related to a problem? Please describe.

No, just am improvement

Describe the solution you'd like

nu shell introduces a data/cache dir, see https://www.nushell.sh/blog/2024-06-25-nushell_0_95_0.html

Those are currently not available to be used in nur inside the .nur folder.

Describe alternatives you've considered

We could just not support this, but then nu and nur would feel more different.