Test suite xfail tracking

[tomwhite]

This is a list of work needed to fix the xfails and TODOs in https://github.com/cubed-dev/cubed-xarray/blob/main/cubed_xarray/tests/test_xarray.py

Cubed

• [x] https://github.com/cubed-dev/cubed/pull/546
• [ ] https://github.com/cubed-dev/cubed/pull/545
• [ ] https://github.com/cubed-dev/cubed/issues/153
• [x] https://github.com/cubed-dev/cubed/issues/29

Xarray

• [x] https://github.com/pydata/xarray/pull/9326

[More to be added over time...]