mag cal improvements (#13487)
* mag cal improvements
reduced threshold to start updating the previous cal
LED0 goes 'solid' only when the calibration start threshold is met
Don't zero previous Cal values until the update threshold is met
Mag_calib debug shows cal values at zero unltil they start being updated.
* beep ready, acc_calibration, and gyro_calibrated, for audio feedback
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* improvements, thanks to feedback from PL
* change magCalEndTimeUs to magCalProcessEndTimeUs
* make process names more obvious
* use static boolean for initation and termination
* magCalProcessEndTimeUs to magCalEndTime
* LED ON, not toggle