Fixes #587: unify project requirements around setup.cfg (#873)

Remove redundant requirements.txt, requirements-dev.txt, and
docs/docs-requirements.txt — all deps are already declared in setup.cfg
extras. Clean up pyproject.toml check-manifest ignore list accordingly
and bump python_requires to >=3.12 to match CI.

Author: brendancol

docs/docs-requirements.txt

@@ -15,8 +15,6 @@ ignore = [
     'CONTRIBUTING.md',
     'Citation-styles.md',
     'RELEASE.md',
-    'requirements-dev.txt',
-    'requirements.txt',
     'test_examples_cli.py',
     'tox.ini',
     'benchmarks/*',

pyproject.toml

@@ -24,7 +24,7 @@ install_requires =
     xarray
     numpy
 packages = find:
-python_requires = >=3.8
+python_requires = >=3.12
 setup_requires = setuptools_scm
 zip_safe = False