CDAT Migration Phase 2: Refactor `diurnal_cycle` set

[tomvothecoder]

• Closes #666

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules

If applicable:

• [x] New and existing unit tests pass with my changes (locally and CI/CD build)
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [ ] I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)

[tomvothecoder]

6/27/24

• [x] Compare plots
  • [x] Fix colormaps being smaller
  • [x] Fix y axis being smaller
  • [x] Fix x axis not starting at 0W
  • [x] Fix x axis being condensed in the middle
• [x] Make sure build passes

[tomvothecoder]

Just an FYI @chengzhuzhang that this PR is complete. I added a new template_cdat_regression_testing_png.ipynb notebook that compares the plots for main and dev to validate that refactored plotters. This notebook can be used for future sets if desired.

In this case, both the regression test for .nc and .png are identical across branches. I will merge once the build passes.