DM-22287: Make inheritDoc more robust and add tests

[timj]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Patch coverage: 80.35% and project coverage change: -0.04% ⚠️

Comparison is base (f0e1c1a) 94.45% compared to head (447bd5e) 94.41%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #171      +/-   ##
==========================================
- Coverage   94.45%   94.41%   -0.04%     
==========================================
  Files          45       46       +1     
  Lines        3100     3154      +54     
==========================================
+ Hits         2928     2978      +50     
- Misses        172      176       +4     

Files Changed	Coverage Δ
tests/test_classes.py	98.80% <ø> (ø)
tests/test_db_auth.py	100.00% <ø> (ø)
tests/test_decorators.py	100.00% <ø> (ø)
tests/test_deprecated.py	100.00% <ø> (ø)
tests/test_doImport.py	100.00% <ø> (ø)
tests/test_ellipsis.py	100.00% <ø> (ø)
tests/test_executables.py	100.00% <ø> (ø)
tests/test_getPackageDir.py	66.66% <ø> (ø)
tests/test_getTempFilePath.py	100.00% <ø> (ø)
tests/test_import.py	100.00% <ø> (ø)
... and 13 more

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[andy-slac]

Looks good, a couple of minor comments.