Add Race game mode

[garsipal]

Here's how I envision it:

• finish line entity: introduce a finish line entity with a radius. When a player crosses this finish line, they get teleported back to a spawn point and a new lap is added to their record;
• checkpoint entity: implement checkpoint entities (with a radius) to ensure that if a player dies, they can respawn from the most recent checkpoint they reached;
• lap limit variable: create a variable that allows the server creator to define the maximum number of laps required to determine the winner;
• scoring system: each time a player finishes a lap, the system records the number of seconds it took them to complete that lap and adds these seconds to their overall points;
• winner determination: the player with the fewest points, indicating they completed laps in the least time, wins the match once the maximum lap limit is reached;