Implement longest_positive_streak with tests and CI

[google-labs-jules]

This pull request introduces the longest_positive_streak function, which calculates the length of the longest run of consecutive positive integers in a list.

It includes:

• The streak.py module containing the function.
• A comprehensive pytest test suite in tests/test_streak.py.
• A GitHub Actions workflow (.github/workflows/pytest.yml) to run tests automatically on push and pull requests.

Verification Number: 47365578

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PR created automatically by Jules for task 1065509268945804584

[google-labs-jules]

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