Fix RANSAC-breaking bug in RANSAC correlation window chunking code

[a-hurst]

PR Description

Partially addresses #41 and #65. Basically, the existing code incorrectly splits the full EEG data into window-sized chunks for RANSAC correlation. For convenience I'm copying my explanation/illustration from #65 below:

What we want it to do is take data like this (where A, B, and C are different channels):

[['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8'],
 ['B1', 'B2', 'B3', 'B4', 'B5', 'B6', 'B7', 'B8'],
 ['C1', 'C2', 'C3', 'C4', 'C5', 'C6', 'C7', 'C8']]

... and reshape it into this (where the number of correlation windows is 4, and there are 2 samples per window):

[[['A1', 'A2'],
  ['B1', 'B2'],
  ['C1', 'C2']],

 [['A3', 'A4'],
  ['B3', 'B4'],
  ['C3', 'C4']],

 [['A5', 'A6'],
  ['B5', 'B6'],
  ['C5', 'C6']],

 [['A7', 'A8'],
  ['B7', 'B8'],
  ['C7', 'C8']]]

...such that when you iterate over the first axis, the windows of data look like the above chunks.

Instead, the PyPREP code above generates this:

[[['A1', 'A2', 'A3', 'A4'],
  ['A5', 'A6', 'A7', 'A8']],

 [['B1', 'B2', 'B3', 'B4'],
  ['B5', 'B6', 'B7', 'B8']],

 [['C1', 'C2', 'C3', 'C4'],
  ['C5', 'C6', 'C7', 'C8']]]

... which is then sliced along the last axis, resulting in windows of data like this:

[[['A1', 'A5'],
  ['B1', 'B5'],
  ['C1', 'C5']],

 [['A2', 'A6'],
  ['B2', 'B6'],
  ['C2', 'C6']],

 [['A3', 'A7'],
  ['B3', 'B7'],
  ['C3', 'C7']],

 [['A4', 'A8'],
  ['B4', 'B8'],
  ['C4', 'C8']]]

The current PR fixes things to work as intended.

Merge Checklist

• the PR has been reviewed and all comments are resolved
• all CI checks pass
• (if applicable): the PR description includes the phrase closes #<issue-number> to automatically close an issue
• (if applicable): bug fixes, new features, or API changes are documented in whats_new.rst

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@032cad1). Click here to learn what that means.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master      #67   +/-   ##
=========================================
  Coverage          ?   97.00%           
=========================================
  Files             ?        7           
  Lines             ?      568           
  Branches          ?        0           
=========================================
  Hits              ?      551           
  Misses            ?       17           
  Partials          ?        0           

Impacted Files	Coverage Δ
pyprep/ransac.py	97.24% <100.00%> (ø)

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[a-hurst]

What's absolutely wild to me is that the RANSAC unit tests still worked totally fine despite this bug. If you can think of an improved method of unit-testing RANSAC, I can add that to this PR request as well: otherwise, we can just wait for the testing-vs-MATLAB CI updates.

[sappelhoff]

I don't have an idea for a unit test right now ... currently I am fully relying on your local tests against Matlab PREP :)

it'd be great to get those tests online soon.

The best would of course be to do that directly in CI, as we discuss in #49