get Block State
Returns the block state present at the given position.
Does not create any necessary chunk or section. Will throw AnvilException if the chunk does not exist (an empty section is considered full of air)
X,Y,Z are in absolute coordinates
Throws
if x,y,z is not a valid position inside this region
if the chunk corresponding to x,z does not exist in this region (ie not loaded by the game, nor created and waiting for saving with this lib)