Switch from pkg_resources (deprecated) to importlib

[xylar]

This pull request updates the way package resources are located in the pcmdi_metrics package by replacing the deprecated pkg_resources with importlib.metadata. The changes affect both the resource location logic and related tests, ensuring compatibility with modern Python packaging practices.

Migration from pkg_resources to importlib.metadata:

• Updated pcmdi_metrics/resources.py to use importlib.metadata instead of pkg_resources for locating package data files, specifically replacing pkg_resources.resource_filename with metadata.distribution(...).locate_file(...). [1] [2]

Test updates for new resource location logic:

• Refactored tests in tests/test_resources.py to mock importlib.metadata.distribution instead of pkg_resources.resource_filename and pkg_resources.Requirement.parse, including the use of a dummy distribution object for resource location. [1] [2]

[xylar]

@lee1043, this is also ready for review. Less critical for E3SM-Unified but a good idea to take care of any deprecation warnings before they start breaking things.

[forsyth2]

For reference, this relates to the observations at E3SM-Project/zppy-interfaces#25 (comment)

[lee1043]

@xylar thank you for the PR!

Confirmed that create_land_sea_mask, which use resources of from pcmdi_metrics import resources, works fine with this PR.

from pcmdi_metrics.utils import create_land_sea_mask, create_target_grid
grid = create_target_grid(-90, 90, 0, 360, target_grid_resolution="5x5")
mask = create_land_sea_mask(grid)
mask.plot()

Also, the Demo 1b mean climate notebook that include mean_lcimate_driver.py uses resources works fine too. Merging the PR now.

[xylar]

Thanks @lee1043!