Fix minimal install and tidy up

[ericpre]

Progress of the PR

• Fix minimum install,
• Allow to run test suite without hyperspy and add corresponding build to CI - most of the tests are skipped but this is useful to test import without hyperspy being installed,
• Remove deprecated EMD class in emd plugin,
• Fix teardown test_empad.py module,
• remove leftover traits dependency,
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• add tests,
• ready for review.

[codecov]

Codecov Report

Merging #13 (784f1bd) into main (4ff3f4a) will increase coverage by 6.27%.
The diff coverage is 81.08%.

@@            Coverage Diff             @@
##             main      #13      +/-   ##
==========================================
+ Coverage   76.54%   82.82%   +6.27%     
==========================================
  Files          39       40       +1     
  Lines        8336     8051     -285     
  Branches     1931     1859      -72     
==========================================
+ Hits         6381     6668     +287     
+ Misses       1500      921     -579     
- Partials      455      462       +7     

Impacted Files	Coverage Δ
rsciio/digital_micrograph/api.py	76.09% <ø> (-0.10%)	⬇️
rsciio/emd/api.py	85.46% <50.00%> (+19.48%)	⬆️
rsciio/conftest.py	71.42% <71.42%> (ø)
rsciio/utils/skimage_exposure.py	62.50% <75.00%> (ø)
rsciio/utils/array.py	85.71% <85.71%> (ø)
rsciio/__init__.py	100.00% <100.00%> (ø)
rsciio/image/api.py	91.56% <100.00%> (+24.06%)	⬆️
rsciio/tvips/api.py	98.47% <100.00%> (+<0.01%)	⬆️
rsciio/utils/rgb_tools.py	79.62% <100.00%> (ø)
setup.py
... and 6 more

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[jlaehne]

Great that the coverage could also be increased notably.

[ericpre]

I will leave the coverage improvement for another PR, as this one is already large enough and this is not the primary concern of this PR.