Adding spatial output options to downscale

[CeresBarros]

I was wondering if it'd make sense to add an option to output the downscaled variables as a spatial object instead of a data.table. Perhaps a vector object?

I only foresee one issue at this point, which is the lat of projection/spatial metadata info in the xyz input object. A solution would be to add bbox as an optional argument (from which we'd extract spatial metadata) or a CRS argument.

Thoughts?

[kdaust]

That would probably make sense - would we use sf or terra? So far I've found sf is faster for vector data than terra, but would require adding another dependency. Also - would this be related to providing optional raster output for downscaled variables?

Re: crs, it's required that the input is in epsg:4326, so I think we can just output in that projection.

[CeresBarros]

I would use terra as we're not going to do spatial operations, just convert the data.table to a spatial object.

Good to know about the CRS. That should be documented and checked accordingly -- I'll take care of that.

[CeresBarros]

done in #144