Add unit tests for dispatch_to_qa

[MarkEdmondson1234]

Expands the unit tests for the prep_request_payload function in tests/test_dispatch_to_qa.py to ensure full coverage of all logic paths.

• Adds new test cases to cover scenarios with empty user input, presence of chat history, and stream requests, ensuring comprehensive testing of the prep_request_payload function.
• Utilizes pytest.mark.parametrize to efficiently test multiple input combinations and expected outcomes.
• Employs mocking for external calls (load_config_key and route_endpoint) to maintain test isolation and self-containment.

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:rocket:	This description was created by Ellipsis for commit 786afdf34a8e9e4cf061773166e9d1ab8cec07bd

Summary:

Enhances prep_request_payload unit tests in tests/test_dispatch_to_qa.py to cover additional scenarios, ensuring comprehensive testing.

Key points:

• Expands unit tests in tests/test_dispatch_to_qa.py for prep_request_payload.
• Adds test cases for empty input, chat history, and stream requests.
• Uses pytest.mark.parametrize for multiple scenarios.
• Mocks external calls (load_config_key, route_endpoint).

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