Implement the kill mechanics for players

[Oleksii-Kshenskyi]

The players should be able to kill and eat other players.

• When a player is on a tile next to another player and looking at it, it can attack.
• There is no HP, if a player attacks another player, it's an instakill, and the player that's been hit dies.
• A dead player becomes food (that restores a bit less hunger than actual food). Once a player has been killed, it drops "food" (its corpse) and can be eaten.

[Oleksii-Kshenskyi]

Initial implementation over, but for now this is blocked by #22 because with the existing implementation of player action processing, it's impossible to mutably pull components for two separate player entities due to Rust's borrowing rules.

[Oleksii-Kshenskyi]

The #22 refactor has solved the mutable borrow issue, and the Kill action is working as intended. There is a difference between dying from hunger and dying from another player: when players are killed, they drop food (corpse), but when they die from hunger they essentially become "deactivated" and do not drop food.

I thought about reworking the death from hunger behavior into dropping food too, but logically, if someone dies from hunger, they die emaciated and therefore that creature is not a good meal anymore. So for now, I'll leave this behavior as is.

Due to the kill action working as intended, this can be closed now.