Build 65: new enemy spawn and teleport system

What’s new:

• New enemy spawn & teleportation logic: instead of a fixed distance “spawn circle”, enemies spawn on the edges of the (original) 16:9 viewport with some extra padding. Enemies are teleported closer when they are too far from the edges. Note that Distance.EnemySpawn and Distance.EnemyTeleport properties in the Level ruleset were repurposed for the new system.
• Some balancing; reduced enemy numbers because new teleportation logic (and distances) makes the level a lot more dense.