Add parallel uv pytest matrix runner

Introduce scripts/run-pytest-matrix.py to run pytest across supported
Python versions in parallel via uv.

The runner now:
- keeps per-version virtualenvs under .runner/.venv-*
- wipes only .runner/outcome-*.txt on each run by default
- supports --recreate-envs for full env rebuilds
- stores stdout/stderr for failed runs in .runner/outcome-<version>.txt
- shows a live spinner with white pending/running, early red failure
  hints, and final green/red based on actual exit status

Document the matrix command in README.rst and ignore .runner artifacts.

Author: kaste

.gitignore

@@ -7,3 +7,4 @@ docs/_build
 __pycache__
 .python-version
 mockito/_version.py
+.runner/

README.rst

@@ -87,6 +87,19 @@ to your computer, then run ``uv sync`` in the root directory.  Example usage::
 
     uv run pytest
 
+To run the full supported Python matrix in parallel::
+
+    uv run python scripts/run-pytest-matrix.py
+
+To run only selected versions::
+
+    uv run python scripts/run-pytest-matrix.py -p 3.8 -p 3.14
+
+The matrix runner keeps per-version virtual environments in ``.runner/``
+(``.venv-3.8``, etc.) so runs can execute safely in parallel while only
+``outcome-*.txt`` files are wiped each run.  Use ``--recreate-envs`` to
+rebuild those environments.
+
 Note: development and docs tooling target Python >=3.12, while the library itself
 supports older Python versions at runtime.
 

pyproject.toml

@@ -30,7 +30,9 @@ dev = [
     "ipython>=7.34.0",
     "mypy>=1.4.1",
     "numpy>=1.21.6",
+    "pyyaml>=6.0.2",
     "pytest>=7.4.4",
+    "types-pyyaml>=6.0.12.20241230",
 ]
 docs = [
     "sphinx>=7.4.7; python_version >= '3.12'",