Fix `EELSArctan` gradients

[ericpre]

Same as https://github.com/hyperspy/hyperspy/pull/3388.

Progress of the PR

• [x] Fix EELSArctan gradients,
• [x] Update link to EDS demos in user guide,
• [x] fix API reference of some components,
• [n/a] update user guide (if appropriate),
• [n/a] added tests,
• [x] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• [x] Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:exspy build of this PR (link in github checks)
• [x] ready for review.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.49%. Comparing base (770f06f) to head (41acbcf). Report is 84 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #55 +/- ## ========================================== + Coverage 87.77% 88.49% +0.72% ========================================== Files 67 67 Lines 7287 7286 -1 Branches 1179 1179 ========================================== + Hits 6396 6448 +52 + Misses 626 568 -58 - Partials 265 270 +5 ```

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