Parallelize pytest --collect-only in split_tests.py

[bdraco]

Proposed change

cProfile of the Split tests for full run CI step shows 99.6% of wall time is in the single pytest --collect-only subprocess. Fan it out across os.cpu_count() workers using ProcessPoolExecutor; round-robin chunking keeps each batch roughly equal, and tests/components is expanded one level deeper so the ~1000 integration subdirectories distribute evenly. Bucket output is unchanged because we still parse the same pytest -qq output, just aggregated from multiple invocations.

CI step time vs dev (4-core runner):

                         dev      PR        Δ
Run split_tests.py      309s    147s    -162s

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[Copilot]

Pull request overview

This PR speeds up the CI “Split tests for full run” step by parallelizing pytest --collect-only in script/split_tests.py, fanning out large directories (notably tests/components) into smaller batches collected concurrently.

Changes:

• Run pytest --collect-only across multiple batches in parallel via ProcessPoolExecutor.
• Add path fan-out logic to expand large directories one level deeper (and tests/components to per-integration paths).
• Aggregate multiple pytest collection outputs back into the existing TestFolder/bucket-splitting logic.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[bdraco]

thanks