Lazy load npq

[joshqsumner]

Describe your changes
Lazy Loading NPQ data into an NPQ class in the PSII_Data class per other changes based from #1926 .

Type of update
This is a feature update

Associated issues
Part of #1926

Additional context
This does not update analyze.npq yet, which can be simplified in another PR after these changes.
This follow after of #1972 but does not strictly edit the same class, I'm still marking with merge in order for clarity.

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

DeepSource Code Review

We reviewed changes in 0a9cf06...b0c5b07 on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

See full review on DeepSource ↗

PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene   Coverage

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
Python		Jul 17, 2026 1:23p.m.	Review ↗
Code coverage		Jul 17, 2026 1:23p.m.	Review ↗

Code Coverage Summary

Language	Line Coverage (New Code)	Line Coverage (Overall)
Aggregate	100% [✓ above threshold]	100%
Python	100% [✓ above threshold]	100%

➟ Additional coverage metrics may have been reported. See full coverage report ↗

---

Important

AI Review is run only on demand for your team. We're only showing results of static analysis review right now. To trigger AI Review, comment @deepsourcebot review on this thread.