Add XProj dependency

[scottyhq]

Addresses #13

Also adds some more development notes (I'm new to hatch so took a bit to understand how to use it)

[scottyhq]

To avoid needing to do the import here looking into integrating (https://xproj.readthedocs.io/en/latest/integration.html) into existing code... https://github.com/dcherian/rasterix/blob/fe7dae09b1c6faa4c3af589a22c8fa7e9bd14b14/src/rasterix/raster_index.py#L287-L288

[dcherian]

Nice, please merge whenever you all think this is ready.

[scottyhq]

While this 'works' after talking with @benbovy we're thinking a better strategy to actually address #13 is to not yet have xproj as a dependency and instead focus on this case:

1. Ensure CRS-matching during (exact) alignment of datasets even in cases where a spatial reference coordinate is missing

https://github.com/xarray-contrib/xvec/blob/5affd7ac591bbdef2722c5eac4b976823384e8ed/xvec/index.py#L102-L111

The xproj integration can happen later as it would needed for specific use-cases (xarray-contrib/xproj#25) but not necessarily required as a dependency

[benbovy]

I'm closing this in favor of #31 where I just added the example notebook.