Update Lis2mdlManager and Lsm6dsoManager with best practices

[nateinaction]

Description

This PR updates the Lis2mdlManager and Lsm6dsoManager with learnings from #76.

• We found a built-in method to convert between Zephyr sensor readings and float64 so we no longer need the Helpers class
• We extracted device instantiation to Main.cpp to allow multiple instances of the component to be created.
• We standardize using m_ prefix to signify member variables and use this-> notation whenever referencing them

Related Issues/Tickets

How Has This Been Tested?

Verified component still works:

• Unit tests
• Integration tests
• Z Tests
• Manual testing (describe steps)

Screenshots / Recordings (if applicable)

Checklist

• Written detailed sdd with requirements, channels, ports, commands, telemetry defined and correctly formatted and spelled
• Have written relevant integration tests and have documented them in the sdd
• Have done a code review with
• Have tested this PR on every supported board with correct board definitions

Further Notes / Considerations