Add tests for specific functions

[MarkZH]

Right now, the only tests are integration tests that perform a complete run of lichess_bot_main() to check that there are no errors communicating with an engine and with a mocked version of the lichess.org servers. Individual functions could use unit tests, such as:

• database functions like get_lichess_cloud_move()
• Lichess class methods to make sure they still return expected responses (bot scopes, profile data, bot opponent lists, etc.)

[Riccardo231]

Hello, I'd like to join the project by working on this issue.

[AttackingOrDefending]

Thank you for your interest in contributing to the project! Feel free to work on this issue. Let us know if you have any questions or need clarification on the details.