Curious if I am missing it, but I don't think you have enabled access to the on-board temperature sensor. This is available in the Arduino version and you have the correct address in __init__.py. Could you add this as a property?

BTW: How does this work? In LSM6DS, I can see where you create self.i2c_device(i2c_bus, address) and I assume you read from that, but you never call a read function in the code??? I was going to just add it myself, but was confused by what you were doing.