CDAT Migration Phase 2: Refactor core utilities and lat_lon set (#677)

Refer to the PR for more information because the changelog is massive.

Update build workflow to run on `cdat-migration-fy24` branch

CDAT Migration Phase 2: Add CDAT regression test notebook template and fix GH Actions build (#743)

- Add Makefile for quick access to multiple Python-based commands such as linting, testing, cleaning up cache and build files
- Fix some lingering unit tests failure
- Update `xcdat=0.6.0rc1` to `xcdat >=0.6.0` in `ci.yml`, `dev.yml` and `dev-nompi.yml`
- Add `xskillscore` to `ci.yml`
- Fix `pre-commit` issues

CDAT Migration Phase 2: Regression testing for `lat_lon`, `lat_lon_land`, and `lat_lon_river` (#744)

- Add Makefile that simplifies common development commands (building and installing, testing, etc.)
- Write unit tests to cover all new code for utility functions
  - `dataset_xr.py`, `metrics.py`, `climo_xr.py`, `io.py`, `regrid.py`
- Metrics comparison for  `cdat-migration-fy24` `lat_lon` and `main` branch of `lat_lon` -- `NET_FLUX_SRF` and `RESTOM` have the highest spatial average diffs
- Test run with 3D variables (`_run_3d_diags()`)
  - Fix Python 3.9 bug with using pipe command to represent Union -- doesn't work with `from __future__ import annotations` still
  - Fix subsetting syntax bug using ilev
  - Fix regridding bug where a single plev is passed and xCDAT does not allow generating bounds for coordinates of len <= 1 -- add conditional that just ignores adding new bounds for regridded output datasets, fix related tests
  - Fix accidentally calling save plots and metrics twice in `_get_metrics_by_region()`
- Fix failing integration tests pass in CI/CD
  - Refactor `test_diags.py` -- replace unittest with pytest
  - Refactor `test_all_sets.py` -- replace unittest with pytest
  - Test climatology datasets -- tested with 3d variables using `test_all_sets.py`

CDAT Migration Phase 2: Refactor utilities and CoreParameter methods for reusability across diagnostic sets (#746)

- Move driver type annotations to `type_annotations.py`
- Move `lat_lon_driver._save_data_metrics_and_plots()` to `io.py`
- Update `_save_data_metrics_and_plots` args to accept `plot_func` callable
- Update `metrics.spatial_avg` to return an optionally `xr.DataArray` with `as_list=False`
- Move `parameter` arg to the top in `lat_lon_plot.plot`
- Move `_set_param_output_attrs` and `_set_name_yr_attrs` from `lat_lon_driver` to `CoreParameter` class