Refactor imu.py to run without hardware

[esharnow]

🚀 Feature Request

imu.py currently requires the import of adfruit_bno055, busio, and board libraries, which work with a Raspberry Pi. The imu.py in the sensors module can be refactored to allow testing this module without access to hardware

🔈 Motivation

This will improve the usability of the module to not require the use of hardware for testing