Fix warnings in building of documentation

[kklein]

The rendered version of this PR can be found here.

Status quo

When running make html in datajudge/docs on main, 178 warnings are produced with sphinx 7.3.7.

Few of those warnings are indeed desired in that they hint at problems we'd want to fix, e.g. :

Assertion Message Styling
----------------
/Users/kevinklein/Code/datajudge/docs/source/getting_started.rst:136: WARNING: Title underline too short.

Assertion Message Styling
----------------
/Users/kevinklein/Code/datajudge/docs/source/testing.rst:2: WARNING: Duplicate explicit target name: "here".

Yet, the bulk of the warnings is of one of two forms:

• /Users/kevinklein/Code/datajudge/src/datajudge/requirements.py:docstring of datajudge.requirements.Requirement:19: WARNING: autosummary: stub file not found 'datajudge.Requirement.append'. Check your autosummary_generate setting.
• /Users/kevinklein/Code/datajudge/src/datajudge/requirements.py:docstring of datajudge.requirements.Requirement.insert:21: WARNING: Explicit markup ends without a blank line; unexpected unindent.

Proposed changes

• Address the warnings we'd like to receive in 42f8a50.
• Adapt the configuration of our documentation in 42f8a50.
  • The autosummary: stub file not found 'datajudge.Requirement.append'. Check your autosummary_generate setting. warnings are eliminated by inheriting doc strings for non-overwritten methods from parent classes.
  • The Explicit markup ends without a blank line; unexpected unindent. warnings are eliminated for a reason that's clear to me.

Running make html on this branch creates no more warnings.

Remarks

In order to address the Explicit markup ends without a blank line; unexpected unindent. warnings, I tried adaptations of the doc strings suggested in this stackoverflow thread. Unfortunately it didn't resolve the issue at hand.