feature: Simple heart rate zone / activity tracker

[Andersama]

Garmin and other devices categorize heart rate activity into a number of zones, typically 1-5 where per detected "activity" the time or % spent in each zone is logged. From what I've found these zones are calculated typically based on age etc.. but for reference

• Zone 5 [166, inf) bpm
• Zone 4 [148-166) bpm
• Zone 3 [130-148) bpm
• Zone 2 [111-130) bpm
• Zone 1 [93-111) bpm

Since there are only 1440 minutes in a day, a basic version of this might be 5 uint16_ts to track the time in each zone, one uint16_t for the total "activity" time.

[Andersama]

Very barebones screen preview: