CDAT Migration Phase 2: Refactor `zonal_mean_2d()` and `zonal_mean_2d_stratosphere()` sets

[tomvothecoder]

Description

• Closes #655

Summary of Changes

Drivers and Parameters

• zonal_mean_2d_driver.py
  • Refactor based on how other sets are refactored (e.g., lat_lon_driver.py)
  • Use deep copy of ZonalMeanParameter.DEFAULT_PLEVS as default value for default_plevs
• zonal_mean_2d_stratosphere_driver.py
  • Removed unused create_metrics() function
  • Use deep copy of ZonalMeanParameter.DEFAULT_PLEVS as default value for default_plevs
• metrics.py
  • Update all functions to accept optional axis argument to specify axes based on requirements of set
  • Default value of axis is ["X", "Y"]
  • Update _get_weights() to handle Z axis with new _get_z_weights() function
• core_parameter.py
  • Add _is_plevs_set() function to check if plevs attr is set. This method is used to determine whether DEFAULT_PLEVS should be used or not in the run_diags() functions found in the driver modules
• zonal_mean_2d_parameter.py and zonal_mean_2d_stratosphere_parameter.py
  • Update plevs attr to use deep copy of DEFAULT_PLEVS defined in each file

Plotting

• plot/utils.py
  • Change PLOT_TITLE and PLOT_SIDE_TITLE dictionaries to MAIN_TITLE_FONTSIZE and SECONDARY_TITLE_FONTSIZE floats
  • Update _save_plot() to accept panel_configs and border_padding args (can vary per set)
  • Extract smaller, reusable functions from _add_color_map() that can be reused when refactoring plot modules for other sets
  • New functions include: _get_c_levels_and_norm(), _add_contour_plot(), _configure_titles(), _configure_x_and_y_axes(), _add_cbar(), _add_min_mean_max_text(), _add_rmse_corr_text()
  • Update _get_contour_label_format_and_pad() to handle float values <0.01 and <0.2
• zonal_mean_2d_plot.py
  • Refactor plot() and _add_colormap() functions based on how other sets are refactored (e.g., lat_lon_plot.py)
  • _Note, this version of _add_colormap() has some subtle differences compared to plot.utils._add_colormap(), which is why I implemented a unique version here (e.g., operates on plevs Z axis)_
• zonal_mean_2d_stratosphere_plot.py
  • Update args passed to plotter

Misc.

• Related to #785

Checklist

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

If applicable:

• [ ] 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
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] 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]

Thanks for the PR. I just have some minor comments and clarification questions. Other then that, maybe to have another regression test for zonal_mean_2d_stratosphere() just in case..

I performed a regression test using zonal_mean_2d_stratosphere(). All variables except two are within the accepted relative tolerance: MERRA2-U-SON and MERRA-U-JJA. Only 16/3610 and 15/3610 elements are mismatched.

Comparing:
/global/cfs/projectdirs/e3sm/e3sm_diags_cdat_test/655-zonal-mean-2d-stratosphere/zonal_mean_2d_stratosphere/MERRA2/MERRA2-U-SON-global_ref.nc
 /global/cfs/projectdirs/e3sm/e3sm_diags_cdat_test/main/zonal_mean_2d_stratosphere/MERRA2/MERRA2-U-SON-global_ref.nc

Not equal to tolerance rtol=1e-05, atol=0

Mismatched elements: 16 / 3610 (0.443%)
Max absolute difference: 1.12679693e-07
Max relative difference: 0.06101062
 x: array([[ 6.962348e-07,  8.762654e-01,  1.605988e+00, ...,  2.470426e+00,
         1.311890e+00,  1.454603e-06],
       [ 1.235800e-06,  1.004880e+00,  1.845646e+00, ...,  2.164340e+00,...
 y: array([[ 6.962348e-07,  8.762654e-01,  1.605988e+00, ...,  2.470426e+00,
         1.311890e+00,  1.454603e-06],
       [ 1.227703e-06,  1.004880e+00,  1.845646e+00, ...,  2.164340e+00,...
Comparing:
/global/cfs/projectdirs/e3sm/e3sm_diags_cdat_test/655-zonal-mean-2d-stratosphere/zonal_mean_2d_stratosphere/MERRA2/MERRA2-U-JJA-global_ref.nc
 /global/cfs/projectdirs/e3sm/e3sm_diags_cdat_test/main/zonal_mean_2d_stratosphere/MERRA2/MERRA2-U-JJA-global_ref.nc

Not equal to tolerance rtol=1e-05, atol=0

Mismatched elements: 15 / 3610 (0.416%)
Max absolute difference: 2.09578261e-07
Max relative difference: 0.00898989
 x: array([[-9.994902e-07,  1.855954e+00,  3.415055e+00, ..., -1.025078e+00,
        -5.548744e-01, -9.440600e-07],
       [-9.595097e-07,  1.685548e+00,  3.103145e+00, ..., -8.308557e-01,...
 y: array([[-9.994902e-07,  1.855954e+00,  3.415055e+00, ..., -1.025078e+00,
        -5.548744e-01, -9.440600e-07],
       [-9.595177e-07,  1.685548e+00,  3.103145e+00, ..., -8.308557e-01,...

I opened a GitHub issue to debug these variables later. I will merge this PR once the build passes.