Adopt RosettaSciIO's plugin design

[hakonanes]

Description of the change

This PR addresses the part of #650 concerning IO. It replaces #651.

The PR focuses on IO only, leaving updates of markers for another PR. Therefore, all tests related to markers are allowed to fail in this PR.

Progress of the PR

• Docstrings for all functions
• Unit tests with pytest for all lines
• Clean code style by running black via pre-commit
• IO tests pass
• All other but marker tests pass
• All docs apart from marker-related docs build as before
• Explore simplifying support of H/ZSPY write plugins in our save() methods

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• New contributors are added to kikuchipy/__init__.py and .zenodo.json.

[ericpre]

Okay, this is because of the way of the save method is overloaded. The changes still rely on private API, because rosettasciio API does have any public API on file format look-up, etc. As of today, it is expected to be used as follow:

from rsciio.hspy import file_writer
file_writer("beautifulplumage.hspy", fdict)

From a quick look, it seems that there are two formats that are supported for writting (nordif and kikuchipy_h5ebsd), so an alternative could be that you try to save to these based on the extension and otherwise fall back to BaseSignal.save? This has the benefit of not relying on private API and is simple.

Longer term, it would make sense to move these to rosettasciio, because the idea is to have the IO code in a standalone library and this will avoid the current issue.

[hakonanes]

Your solution sounds reasonable, I'll try that once all IO tests pass.

[hakonanes]

The changes still rely on private API

I believe our IO depended on public HyperSpy <2 API. Which after moved to Rosetta became private. Not saying we should still use it, though.

[hakonanes]

an alternative could be that you try to save to these based on the extension and otherwise fall back to BaseSignal.save

Thanks for this suggestion, much cleaner solution. No explicit dependency on Rosetta needed either.

[hakonanes]

Not quite, a bit more work to get rid of the Rosetta dependency...