docs: reflect pytest --command support

[gnufede]

What

Documents that since release 1.7.0, Python/pytest honors --command / DD_TEST_OPTIMIZATION_RUNNER_COMMAND to override the default python -m pytest invocation. PR #123 made PyTest.RunTests and DiscoverTests use commandOverride when
set, so callers can run the pytest console script (or a wrapper) instead of python -m pytest. Previously the docs stated pytest ignored --command.

Updates docs/settings.md, docs/running.md, docs/best_practices.md, and README.md to describe the override and retain PYTEST_ADDOPTS guidance for passing extra pytest flags.

Why

python -m pytest sets sys.argv[0] to pytest's __main__.py, which ddtrace's detect_service incorrectly treats as a test file path, yielding service='pytest' instead of the module name. The pytest console script sets
argv[0]='pytest', which detect_service skips, so service inference is correct. With this change, projects set DD_TEST_OPTIMIZATION_RUNNER_COMMAND=pytest and ddtest runs pytest <files>.

The docs previously claimed pytest ignored --command and that PYTEST_ADDOPTS was the only way to customize the pytest invocation, which is no longer accurate.

Testing

Tested internally in dd-trace-py CI

[datadog-datadog-us1-prod]

More details

The changed documents match the pytest command override behavior. The review found no incorrect or conflicting guidance.

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🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 86.47% (+0.03%)

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