strip out xr.Dataset type hints

[AUdaltsova]

Pull Request

Description

All data sources are currently loaded as xr.DataArray, so stripped out xr.Dataset hints where appropriate (basically everywhere except for functions called inside loaders that do operate on a ds)

How Has This Been Tested?

Ran built-in tests

• [X] Yes

Checklist:

• [X] My code follows OCF's coding style guidelines
• [X] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [X] I have checked my code and corrected any misspellings