Update findSpectatableGames to include player details in the response.

[Hakaabi]

Update the findSpectatableGames helper function to include player details in the game response. Ensure that the response structure matches the requirements for the game list display.

Tasks:

-Add the .populate('players') call to the query in findSpectatableGames.
-Modify the function to transform the player data to include only id and username.
-Test the updated function to ensure it works as expected.

Acceptance Criteria:
-The findSpectatableGames helper function must include a .populate('players') call in its query to retrieve player data for each game.
-The function must return a players array where each player's data is transformed to include only id and username, ensuring no extraneous data is exposed.
-Backend tests must verify the correctness of the updated response structure, including edge cases (no players, one player, two players), and confirm the function operates as expected.