Migrate test pipeline to Github - #544

Run the test suite on GitHub Actions across Ubuntu, macOS, and Windows,
driving pytest directly with uv (uv sync + uv run pytest) rather than tox.
The pytest configuration in tox.ini [pytest] is reused as-is, so junit and
coverage reports are still produced; test results are published with
mikepenz/action-junit-report. The Azure Pipelines test job is left in place
for now, until deployment is also migrated.

Pin the Python version via a tracked .python-version file instead of
hardcoding it, and update the docs workflow to rely on it as well.

PyPI publishing is now handled by the GitHub Actions publish workflow, so
drop the Azure deploy job to avoid two systems publishing to PyPI on main.
The Azure tox test job is kept for now.

Add a CodeCoverageSummary step that renders the Cobertura coverage.xml into
the GitHub Actions job summary, so coverage is visible in the run without
posting a PR comment. Run it only on the Linux matrix leg (Docker action;
coverage is identical across platforms) and never fail the build on it.

Replace the irongut/CodeCoverageSummary Docker action with coverage.py's
built-in markdown report piped to the Actions job summary. This drops a
third-party dependency, stays in sync with the installed coverage version,
and needs no Docker.

CI has fully migrated to GitHub Actions (tests, docs, and PyPI publishing),
so drop azure-pipelines.yml and its dead build-status badge from the README.

Extract the [pytest] section from tox.ini into a dedicated pytest.ini at the
repo root. It stays at the root (not tests/) so testpaths spanning tests/ and
docs/ still resolve. tox continues to read this config for local runs.

Remove tox.ini now that CI runs pytest and Sphinx directly via uv. Update the
README to run the suite with pip/pytest or uv (matching CI) instead of tox,
and refresh the workflow comment that referenced tox.ini.

Restructure installation and usage around uv (uv add, editable installs,
branch dependencies), and move the test instructions to run via
uv run --extra test pytest, matching the GitHub Actions CI. Group advanced
usage and troubleshooting notes together.

networkx (pulled in via hyperopt) requires Python >=3.11, so 3.10 could not
actually resolve the dependency set. Bump requires-python to >=3.11, drop the
3.10 classifier to match the README, and relock.

atomica imports networkx directly (framework and model validation, and the
MCP server), so declare it explicitly rather than relying on it arriving
transitively via hyperopt. The lazy imports in framework.py/model.py are kept
so networkx is only loaded when validation runs.