T361190 introduced the possibility to run the extensions test suite in parallel by splitting the suite into smaller chunks that can be run individually. The original implementation was directly in Python in Quibble.

With T365976, we now have the option to split the tests using a composer command. Migrate Quibble to use this PHP implementation and remove the Python implementation.

Acceptance Criteria

• Quibble (QUIBBLE_PHPUNIT_PARALLEL) uses the new composer command to split the test suite
• Python implementation of test suite splitting is removed from Quibble