[Feature Request] Add support for external Qwiic BMI270 and ICM-20948 IMUs

[nairck]

Please add support for using external Qwiic-connected BMI270 and ICM-20948 IMU sensors on addresses 0x68 and 0x69, respectively. The internal IMU may not be functional in some units, and it would be useful to support external IMUs as standalone loggable sensors, like other Qwiic modules. This would enhance compatibility for logging applications where the onboard SPI IMU fails or is not present.

These are common sensors, have QWIIC connector breakout boards already made by Sparkfun, and both have existing Arduino libraries:

• BMI270 library
• ICM-20948 library

Please treat these as regular sensors, not replacements for the onboard IMU. Auto-initialize if present, and log XYZ acceleration + gyro + mag (for 9dof IMU).