Move unit tests out of mpas_tools

[xylar]

This pull request involves significant cleanup and restructuring of the testing framework for the conda_package, as well as improvements to code readability and maintainability. The most important changes include renaming and reorganizing test files, replacing hardcoded file paths with utility functions, and updating string formatting to use f-strings for better readability.

Test Framework Restructuring:

• Renaming and reorganizing test files: All test files under conda_package/mpas_tools/tests/ have been moved to conda_package/tests/ to streamline the directory structure. Corresponding imports and references have been updated.

• Replacing hardcoded file paths with utility functions: Hardcoded paths for test data files (e.g., mesh_tools/mesh_conversion_tools/test/mesh.QU.1920km.151026.nc) have been replaced with calls to get_test_data_file() to improve flexibility and maintainability.

Code Readability Improvements:

• Switching to f-strings for string formatting: Legacy string formatting (e.g., .format()) has been replaced with f-strings across multiple test files for better readability and consistency.

• Reorganizing imports: Imports have been reordered and grouped logically to improve clarity in test files.

Documentation Updates:

• Removal of outdated references in documentation: References to tests in the documentation (conda_package/docs/api.rst and conda_package/docs/cime.rst) have been removed or updated to reflect the new structure.