build: move the pytest settings into pyproject.toml

[blaipr]

Sits on #958, which edits .coveragerc; merge that first. The .coveragerc move is a separate pull request so the two can be reviewed, and reverted, on their own.

pyproject.toml already owns [tool.setuptools], [tool.setuptools_scm] and [tool.ruff], so pytest.ini becomes [tool.pytest.ini_options] and the file goes. tox.ini and .yamllint stay, since neither reads pyproject.toml.

One value changed, and it fixes 14 collection errors

pytest.ini set python_files to every .py, so collecting imported the whole repository looking for tests. That includes modules which parse argv at import time, and one of them takes the run down rather than reporting:

File "/awx_devel/tools/data_generators/rbac_dummy_data_generator.py", line 88, in <module>
    options, remainder = parser.parse_args()
  ...
INTERNALERROR> SystemExit: 2

Nobody has seen it because CI collects named paths rather than the tree.

Nothing needed the wider net. I checked every .py in the repository: not one file outside pytest's own patterns defines a test. The only two that look like they do are fixtures named test_* inside a conftest.py, which pytest never collects as a module anyway. So python_files is pytest's default now:

collecting the whole tree	tests	errors	time
before	4,020	14	26.1s
after	4,020	0	8.5s

Same tests, no errors, and collection is three times faster because pytest stops importing the codebase to look for them.

Checks

• All eight markers still register (ac, survey, inventory_import, defined_in_file, job_permissions, activity_stream_access, job_runtime_vars, fixture_args).
• awx/main/tests/unit: passing.
• README.md, CONTRIBUTING.md and .github/copilot-instructions.md pointed readers at pytest.ini and now point at pyproject.toml.