test: Psl unit test cps v2

[Prachig-Microsoft]

This pull request introduces significant improvements to the Python testing infrastructure and adds comprehensive unit tests for the ContentProcessor backend. The main changes include expanding the GitHub Actions workflow to support separate test jobs for core logic, API, and workflow components, upgrading the Python version, and adding new unit tests and coverage configuration files.

CI Workflow Enhancements:

• Added new test jobs for API and workflow components in the .github/workflows/test.yml, ensuring each major backend module is tested independently with coverage enforcement.
• Updated the backend test discovery and execution logic to reflect new directory structures and ignore specific test files as needed.
• Upgraded the Python version used in CI from 3.11 to 3.12 for all jobs.
• Included a new branch (psl-unit-test-cps-v2) in the workflow trigger list.

Testing and Coverage Configuration:

• Added a .coveragerc file in src/tests/ContentProcessor to focus coverage on core business logic and exclude integration components and test files.
• Added a README.md in src/tests/ContentProcessor to document the structure and usage of the core unit tests.

Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

What to Check

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