docs: add error codes + some cleanup

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Add error codes to issue titles. Also reword a bit transitive dependencies example, and remove a leftover from 90b5801.

[codecov]

Codecov Report

Merging #367 (76fc1dd) into main (eaf9546) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main    #367   +/-   ##
=====================================
  Coverage   96.8%   96.8%           
=====================================
  Files         37      37           
  Lines       1029    1029           
  Branches     206     206           
=====================================
  Hits         997     997           
  Misses        20      20           
  Partials      12      12