[testing, CI] fix coverage statistics issue caused by test_common.py tracer patching

[icfaust]

Description

Python code coverage has been introduced in #2222 and #2225. Some code, while properly covered with tests, was showing incorrect coverage. It was discovered that the tracing used in test_common.py interferes with the tracing collected by pytest-cov. Any tests alphabetically after test_common.py have been neglected in codecov and by coverage.py. Correcting this can be done by tracing the estimators in a separate process and passing the data back to the pytest-cov parent process.

This has been implemented using python multiprocessing due to the time overhead of loading sklearnex for each estimator and method. The process persists for the period of all test_common.py tests as a daemon process. The test passing/xfail/etc rate has been verified to match to main.

No performance metrics are generated due to purely for testing and CI.

The effectiveness of this change can be observed by the ~1.2% improvement in code coverage (as indirect changes).

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• I have reviewed my changes thoroughly before submitting this pull request.
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Performance

• I have measured performance for affected algorithms using scikit-learn_bench and provided at least summary table with measured data, if performance change is expected.
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• I have extended benchmarking suite and provided corresponding scikit-learn_bench PR if new measurable functionality was introduced in this PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Flag	Coverage Δ
github	84.39% <ø> (+1.20%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 13 files with indirect coverage changes

[icfaust]

/intelci: run

[icfaust]

/intelci: run