Map Clean Up

[CSSFrancis]

Description of the change

This removes the parallel argument for the map function.

• Removes the parallel argument
• Rename max_workers to num_workers to be consistent with dask
• Adds more documentation on setting the dask backend
• Adds navigation_chunk argument for setting the chunks with a non-lazy signal
• Fix axes handling when the function to be mapped can be applied to the whole dataset (_map_all code path) - typically when it has the axis or axes keyword argument and the function argument are not navigation coordinate dependent.

Progress of the PR

• Change implemented (can be split into several points),
• update docstring (if appropriate),
• 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

Patch coverage: 93.43% and project coverage change: -0.01% ⚠️

Comparison is base (56a5db3) 81.30% compared to head (1b2f0cc) 81.30%.
Report is 83 commits behind head on RELEASE_next_major.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           RELEASE_next_major    #3198      +/-   ##
======================================================
- Coverage               81.30%   81.30%   -0.01%     
======================================================
  Files                     176      173       -3     
  Lines                   24406    24207     -199     
  Branches                 5681     5626      -55     
======================================================
- Hits                    19843    19681     -162     
+ Misses                   3258     3224      -34     
+ Partials                 1305     1302       -3     

Files Changed	Coverage Δ
hyperspy/_lazy_signals.py	92.30% <ø> (-0.55%)	⬇️
hyperspy/datasets/example_signals.py	100.00% <ø> (ø)
hyperspy/defaults_parser.py	68.25% <ø> (-0.25%)	⬇️
hyperspy/misc/example_signals_loading.py	100.00% <ø> (ø)
hyperspy/signals.py	100.00% <ø> (ø)
hyperspy/drawing/_widgets/horizontal_line.py	86.95% <66.66%> (-3.05%)	⬇️
hyperspy/drawing/_widgets/rectangles.py	41.24% <66.66%> (+0.65%)	⬆️
hyperspy/drawing/_widgets/vertical_line.py	91.30% <66.66%> (+1.30%)	⬆️
hyperspy/drawing/widget.py	73.19% <80.00%> (+2.80%)	⬆️
hyperspy/signal.py	77.58% <81.81%> (-0.15%)	⬇️
... and 10 more

... and 3 files with indirect coverage changes

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[ericpre]

@CSSFrancis, I initially wanted to rebase to review and finish this PR, but got sidetracked with the documentation and spotted a bug with _map_all. Can you please have a quick look to check that my changes are sensible?
Other than that it looks good to me.

[ericpre]

Move this example here, the example of the gallery needs to be run and I am not that it would be possible/easy on CI.

[CSSFrancis]

Yea I think maybe the distributed workflow would run but not the slurm workflow so you are right we should move it.

[CSSFrancis]

@ericpre I'll look at this a little later today or tomorrow. I've been pretty busy the last week or so and haven't been on top of some of these PRs. :)

I'll have some time the next month to help with the major release.

[ericpre]

@CSSFrancis, are you happy with my changes to this PR? If so, can you please merge it?

[CSSFrancis]

@ericpre I'm going to check that the documentation builds this time and then I can merge this. Your changes look good to me!