Tool transformation previews

LevelRef::block_transform previews a tool against a loaded block in the server level in place. Pass the live player, hand, stack, position and hit; the owned result describes the new state, relative durability cost, sound, loot and particle. The call does not apply the result. It fires block_tool_modification with ToolUse::simulated set to true: listeners must not change the level during a simulation. A stale or unavailable player or level, unloaded position, invalid face, or tool with no transformation returns None. The real action fires the same hook with simulated set to false.