Item Despawn

When there are too many items on the ground, some of them may periodically despawn (i.e. they are removed from the world).

Carriable items on the ground are eligible for despawning when:
 * The item has never been reserved (clicked on by the player or targeted by a Find command from a bot)
 * The item was not on the ground when the world was generated
 * The item is not one of the following: Stone, Clay, Metal Ore, Coal, Colonist, or an unstackable animal

The game keeps track of a separate three-minute timer (one-minute for Dung) on each item that is eligible for despawning. When an item's timer reaches zero, it is removed from the game, but these timers will only count down when there are 20 or more items of the same type on the despawn list.