let encode_nbt has a target type. and add a function for NBT type probing

[17183248569]

this is a small pr, and it is to add this 2 function:

nbt_type(nbt_value [, nbt_path] ) -> return the nbt type of a NBT value.
get_as_nbt(nbt_value , nbt_path ) -> same as nbt_value:nbt_path , but will not try to cast it to scarpet value.

and allows encode_nbt s second argument be 'short' / 'byte' / 'byte_array'...... as the target type.