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.)