Coerce wavelength key types for json dump

[joshqsumner]

Describe your changes
Coerces np.integer types to int after an annoying error that I got.

Type of update
This is a bug fix.

Associated issues
Closes #1938

Additional context
None

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 ce0b36e...d26c5d8 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		Jun 9, 2026 6:33p.m.	Review ↗
Code coverage		Jun 9, 2026 6:33p.m.	Review ↗

Code Coverage Summary

Language	Line Coverage (New Code)	Line Coverage (Overall)
Aggregate	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]
Python	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]

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

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