Fixed doc site build fails

[kennethshsu]

What does this pull request do?

Restored the doc site to its former glory!!!

This review might be a bit hard to read, but most of it is fixing the link code needed by readthedocs.

Relevant Github ticket(s)?

None, but the site should be alive after merging. It's already live on the side branch.

---

Note

Low Risk
Low risk: changes are confined to documentation build configuration and a small Sphinx extension import path fix, with no runtime/library behavior impact.

Overview
Fixes doc-site builds by ensuring the local docs/_ext/linkcode.py extension can be imported in standalone Sphinx/Read the Docs builds.

This updates Jupyter Book/Sphinx config to register linkcode correctly, prepends docs/_ext onto sys.path in docs/conf.py (and adds docs/prep_sphinx_conf.py to auto-inject that block after jupyter-book config sphinx runs), and adjusts tests/pytest config so the extension is importable during CI. Also refreshes the PR template headings.

^{Reviewed by Cursor Bugbot for commit 5f23ed5. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.25%. Comparing base (7200ec2) to head (5f23ed5).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #733   +/-   ##
=======================================
  Coverage   85.25%   85.25%           
=======================================
  Files          85       85           
  Lines        4952     4952           
  Branches      645      645           
=======================================
  Hits         4222     4222           
  Misses        521      521           
  Partials      209      209           

Flag	Coverage Δ
unittests	85.25% <ø> (ø)

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