Sky Whales

Fixes

• Whales no longer suffocate themselves. In combat the whale steers its body straight at targets with no terrain avoidance, so it could clip cliffs/ravines and take IN_WALL damage until it died. Whales now ignore suffocation damage.
• Corpses now reliably despawn ~20 minutes after death, including when their chunk has unloaded. Previously abandoned corpses could linger indefinitely.
• Fewer whales over the ocean. Per-chunk spawn cap lowered from 2 to 1, and whales now despawn when no player is nearby instead of persisting forever, so they no longer accumulate into dozens. (Name-tag a whale to keep it.)