Support for multi-key calibrations

Some kinds of calibrations, e.g. for a treadmill, might have multiple calibrations that are keyed off of different features. Like a "treadmill" calibration and an "encoder" calibration. Another example is a load cell device which might be constructed from multiple cells.

Some possible alternatives:

- For a single device_name support multiple input/output pairings by using dictionaries `input/output: dict[str, List[str, float]`
- Put entire calibrations into a key list, so `calibrations: dict[str, Calibration]`, this has the downside that Calibration already inherits from `DeviceConfig`, so we would probably need to pull out the core calibration classes into a `CalibrationBase` or something