add optional deps handling and testing

[atravitz]

Checklist

• All new code is appropriately documented (user-facing code must have complete docstrings).
• Added a news entry, or the changes are not user-facing.
• Ran pre-commit: you can run pre-commit locally or comment on this PR with pre-commit.ci autofix.

Manual Tests: these are slow so don't need to be run every commit, only before merging and when relevant changes are made (generally at reviewer-discretion).

• GPU integration tests
• example notebook testing
• packaging tests: run this for any large feature PRs or PRs that add test data.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[github-actions]

🚨 API breaking changes detected! 🚨
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.03%. Comparing base (f7561cd) to head (85d4d41).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1826      +/-   ##
==========================================
- Coverage   95.27%   93.03%   -2.25%     
==========================================
  Files         201      201              
  Lines       17589    17574      -15     
==========================================
- Hits        16758    16350     -408     
- Misses        831     1224     +393     

Flag	Coverage Δ
fast-tests	93.03% <100.00%> (?)
slow-tests	?

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