Account for games that can be played concurrently in the algorithm

[mrodz]

This line fails for modern inputs to the scheduling algorithm: https://github.com/mrodz/fieldz-desktop/blob/97e8b2eaea4781b3a14d02ae0471747272fce815/backend/src/algorithm/v2.rs#L192

There can now be multiple games being played in parallel, so the one-game-per-time-slot rule is kaput.