use importlib.resources instead of pkg_resources

[orbeckst]

fix #282

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 0.00%. Comparing base (4574592) to head (51a1e79).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
gromacs/config.py	0.00%	1 Missing ⚠️
gromacs/fileformats/xvg.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #284       +/-   ##
==========================================
- Coverage   69.20%   0.00%   -69.21%     
==========================================
  Files          22      22               
  Lines        3959    3954        -5     
  Branches      717       0      -717     
==========================================
- Hits         2740       0     -2740     
- Misses       1038    3954     +2916     
+ Partials      181       0      -181     

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[orbeckst]

3.9 - 3.11 runners fail with errors such as

==================================== ERRORS ====================================
______________ ERROR collecting tests/fileformats/test_convert.py ______________
tests/fileformats/test_convert.py:12: in <module>
    from gromacs.fileformats import convert
gromacs/__init__.py:216: in <module>
    from . import config
gromacs/config.py:328: in <module>
    templates = _generate_template_dict("templates")
gromacs/config.py:324: in _generate_template_dict
    for entry in resources.files(__name__).joinpath(dirname).iterdir()
../../../micromamba/envs/gromacs_wrapper/lib/python3.11/importlib/resources/_common.py:22: in files
    return from_package(get_package(package))
../../../micromamba/envs/gromacs_wrapper/lib/python3.11/importlib/resources/_common.py:55: in get_package
    raise TypeError(f'{package!r} is not a package')
E   TypeError: 'gromacs.config' is not a package

Python 3.12 works.

[orbeckst]

In 3.12, we can use a module instead of a package as an anchor for importlib.resources.files

Changed in version 3.12: package parameter was renamed to anchor. anchor can now be a non-package module and if omitted will default to the caller’s module. package is still accepted for compatibility but will raise a DeprecationWarning. Consider passing the anchor positionally or using importlib_resources >= 5.10 for a compatible interface on older Pythons.