docs: fix sphinx build for manual part fix

[stevenhua0320]

@sbillinge Ready for review, note that this is the manual fix part of sphinx build, there is also autodoc build break that happens in pdffit, I'm still looking where it fails to import.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.97%. Comparing base (06d1592) to head (b9ae998).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #160   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files           6        6           
  Lines        1270     1270           
=======================================
  Hits         1257     1257           
  Misses         13       13           

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