Fix code snippets in documentation for doctest

[thorbjoernl]

Change Summary

Adds support for doctest and ensures all doctests pass locally. Note that since the doctests examples rely on lustre data, they have not been enabled for the CI testing.

To run doctest when running tests locally add --doctest-modules to your pytest invocation (ie. pytest --doctest-modules)

To have every pytest run use this option automatically, create a pytest.ini with the following content:

[pytest]
addopts = --doctest-modules

Related issue number

closes #1438

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.33%. Comparing base (3867e4b) to head (f38eec6).
Report is 105 commits behind head on main-dev.

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1440      +/-   ##
============================================
- Coverage     78.49%   78.33%   -0.17%     
============================================
  Files           140      140              
  Lines         21299    21413     +114     
============================================
+ Hits          16719    16773      +54     
- Misses         4580     4640      +60     

Flag	Coverage Δ
unittests	78.33% <ø> (-0.17%)	⬇️

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[lewisblake]

Once #1439 fixed, this should be easier, but still a pretty big task

[lewisblake]

LGTM