Xarray IO code and stacking

[phockett]

In XR v2022.6 some base IO code is broken, specifically issue(s) with restacking routines (raw data to XR) and/or dropping selected dims?

To do:

• Retest with XR v2022.3 (OK)
• Test with XR v2022.9 (FAILS)
• Test routines more carefully.
• Rewrite some IO code? Needs a tidy-up in any case. (See also recently added R-matrix IO for possibly better methods.)