Lazy load spc

[joshqsumner]

Describe your changes
Lazy load spectral (SPC) data in a PSII_data instance

Type of update
This is a feature update

Associated issues
Part of #1926

Additional context
Follows after #1986

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 3310a32...2f6e681 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		Aug 4, 2026 4:38p.m.	Review ↗
Code coverage		Aug 4, 2026 4:38p.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 ↗

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