feature 1653 main_v4.1 climo day_interval NA value

[georgemccabe]

Pull Request Testing

• Describe testing already performed for these changes:
  

Added unit tests to ensure NA and integers can be set for day_interval

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

Verify all tests pass

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [No]
  
  Just new unit tests added, all tests should still pass

• Please complete this pull request review by 6/22/2022.
  

Pull Request Checklist

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[j-opatz]

All of the checks passed and the unit tests are behaving as expected.