Add unit tests for chat_history module

[MarkEdmondson1234]

Adds new unit tests for the chat_history module in the sunholo/agents directory, enhancing the test coverage for this module.

• New Test File: Introduces tests/test_chat_history.py containing tests for functions extract_chat_history, embeds_to_json, create_message_element, is_human, is_bot, and is_ai.
• Parametrized Tests: Utilizes pytest.mark.parametrize to efficiently test multiple scenarios for each function, ensuring comprehensive coverage.
• Self-contained Tests: Ensures all tests are self-contained, adhering to the task requirement of not needing external dependencies for execution.

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:rocket:	This description was created by Ellipsis for commit 53bd5b2001e0043042ff22a5575368680db6fe9d

Summary:

Introduces comprehensive unit tests for the chat_history module in sunholo/agents, enhancing test coverage and code reliability.

Key points:

• Adds tests/test_chat_history.py for chat_history module.
• Includes tests for extract_chat_history, embeds_to_json, create_message_element, is_human, is_bot, is_ai.
• Uses pytest.mark.parametrize for multiple scenarios.
• Ensures tests are self-contained, no external dependencies.

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