Xarray-regrid

New contributors:
- kjdoore

Fixed:
- Ensure all attributes are kept upon regridding (dataset, variable and coordinate attrs) ([27](https://github.com/EXCITED-CO2/xarray-regrid/pull/27)).
- The target grid can now have coordinates sorted in decending order, instead of the regridding failing ([29](https://github.com/EXCITED-CO2/xarray-regrid/pull/29)).
- Regridding to larger grid now result in NaNs at locations outside of starting data grid ([33](https://github.com/EXCITED-CO2/xarray-regrid/pull/33)).

Changed:
- Moved to the Ruff formatter, instead of black ([27](https://github.com/EXCITED-CO2/xarray-regrid/pull/27)).

Added:
- CITATION.cff file for Zenodo integration.

Fixed:
- Datasets containing NaN values can now be regridded using the conservative method. This previously produced only NaN values.

Added:
- xarray DataArrays are now supported
- Conservative regridding method, along with a benchmark notebook.
- A "most common value" regridding method, along with a demo notebook.

Changed:
- The API has changed. Regridding is now done with `xr.Dataset.regrid.method()`.
- E.g. `xr.Dataset.regrid.linear()`

First release of `xarray-regrid`, containing:
- the implementation of linear, nearest-neighbor and cubic regridding.
- benchmarks against CDO and xESMF for linear and nearest-neighbor.