activity: store detailed heart data for workouts and sleep

[sahil7886]

Summary

This change saves detailed heart data during a built-in Workout and during detected sleep.

A user can start a Workout as usual. The watch keeps one heart-rate value each second. On watches that support HRV, it also keeps accepted pulse-to-pulse interval (PPI) values. The watch stores this data locally. It does not need a phone connection while the Workout runs.

During a detected overnight sleep period, the watch stores accepted PPI values, one heart-rate value every 30 seconds, and a 30-second motion summary. The normal activity session stays the main Workout summary. These new records add detail to that summary.

Before this change

• Background heart-rate sampling used BPM only. The watch sampled at the user-selected interval: 10 minutes by default, 30 minutes, one hour, or disabled.
• Each background sampling run used a one-second sensor interval. It stopped after 60 seconds or after enough good readings.
• An open Workout requested BPM updates at a one-second interval.
• Workout readings updated the current BPM, heart-rate zones, and the average heart rate in the normal Workout summary.
• Valid BPM readings also entered the general heart-rate log. They were not a separate, clearly bounded Workout dataset.
• The watch did not keep raw PPI values.

After this change

• The existing background heart-rate log and Workout summary behavior stays in place.
• An active Workout saves at most one BPM record per UTC second in a Workout-specific stream.
• On watches with HRV support, an active Workout also saves every accepted PPI value.
• The watch stores this detail locally and sends it through the normal DataLogging transfer.
• Detected overnight sleep also stores PPI values, a BPM value every 30 seconds, and 30-second motion summaries.

What this enables

A companion or analysis tool can:

• Reconstruct the BPM timeline for one specific Workout, without paused time.
• Know when the full Workout dataset is complete.
• Use raw PPI data on supported watches for beat-to-beat and HRV analysis.
• Correlate overnight PPI, BPM, and motion with detected sleep.

This change records and transfers the new detail. It does not add a user-facing chart or insight by itself. A companion-side consumer must read these streams to present the data.

Implementation

• Add three system DataLogging streams: Workout heart rate, Workout PPI, and sleep capture.
• Use versioned, fixed-size records. Each record has a session ID, sequence number, time, value, quality, and state flags.
• Add a final record when a Workout or sleep capture ends. The companion can use this record to know that a stream is complete.
• Keep the Workout PPI stream at its raw accepted values. The watch does not invent missing intervals or calculate new HRV values.
• Start the HRV sensor feature only during an active Workout or sleep capture. Return to BPM-only operation when it ends.
• Make the HRM manager refresh a live sensor subscription after its feature set changes.
• Resume the sleep stream after a reboot. Use a non-zero session ID and sequence gaps to keep replay safe.
• Add unit-test links and fakes for the new telemetry paths.

User effect

• Workout detail stays on the watch until the normal DataLogging transfer can send it.
• Sleep detail can support later analysis without changing the existing activity summary.
• The change adds no public SDK API and no user interface.

Validation

• Rebased onto current Core Devices main; the six commits apply without conflicts.
• Ran gitlint and git diff --check.
• Ran the full local QEMU test suite: ./waf test -k (pass).
• PR CI will also run the project container, QEMU tests, and firmware builds.