Add more tests

[AbhijeetKrishnan]

Currently, there are fewer tests than are ideal. I would like to have more tests to inspire confidence in the package. These tests are based on checking the valid moves available from a game state, as well as checking that the resultant state from a move is correct.

Some examples are -

• If no valid moves are present even with pieces on the board, declare a draw (probably not theoretically possible)
• states in the middle of various capturing sequences

[AbhijeetKrishnan]

Closed due to reliance on PettingZoo's api_test function