fix doc build

[d-chambers]

Description

This PR fixes an issue with the doc build introduced from using a public named tuple in #456.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes.
• documented the new feature with docstrings or appropriate doc page.
• included a test. See testing guidelines.
• your name has been added to the contributors page (docs/contributors.md).
• added the "ready_for_review" tag once the PR is ready to be reviewed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.85%. Comparing base (dc1d36f) to head (1ddf569).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #457   +/-   ##
=======================================
  Coverage   99.85%   99.85%           
=======================================
  Files         115      115           
  Lines        9372     9372           
=======================================
  Hits         9358     9358           
  Misses         14       14           

Flag	Coverage Δ
unittests	99.85% <100.00%> (ø)

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