Add generic pyMC modem telemetry support and preserve modem GPS satellite details

[yellowcooln]

PR Summary

Overview

This PR adds first-class support for consuming diagnostics from a networked pyMC modem HTTP API, including GPS, battery, and solar telemetry.

It also fixes GPS diagnostics for modem-backed GPS sources by preserving detailed satellites.in_view[] records so the UI can correctly plot satellite azimuth, elevation, and SNR data.

The implementation is intentionally modem-generic. New sensor and source names use pymc_modem and modem_http rather than board-specific naming, allowing support for current and future pyMC modem hardware exposing the same /api/stats API.

Changes

Modem HTTP GPS Source

Adds a new GPS source type:

gps:
  source: modem_http

Supported aliases:

• modem_http
• pymc_modem
• http

Features:

• Polls GPS data directly from a pyMC modem HTTP API.
• Supports HTTP Basic Authentication.
• Accepts either a full /api/stats payload or a nested GPS payload.
• Normalizes modem GPS data into the existing repeater GPS diagnostics format.
• Reports modem HTTP failures as GPS source errors without crashing the GPS service.

GPS Satellite Detail Preservation

Preserves detailed modem satellite visibility records:

satellites.in_view[]

Normalizes:

• prn
• elevation_degrees
• azimuth_degrees
• snr_db

Also supports alternate field names:

• elevation
• azimuth
• snr

This fixes an issue where modem-backed GPS sources could report a valid fix and satellite counts while the diagnostics UI displayed zero plottable satellites due to missing azimuth/elevation/SNR data.

New pymc_modem Sensor

Adds a new sensor type:

type: pymc_modem

The sensor reads modem telemetry from the HTTP /api/stats endpoint and exposes:

• GPS enabled state
• GPS fix status
• Latitude / longitude / altitude
• Satellites used and in view
• Date/time
• Speed and course
• Battery voltage
• Solar charging telemetry

The sensor tolerates missing GPS coordinates and optional telemetry fields, allowing use on non-GPS or GPS-disabled modem deployments.

CRC Counter Handling

Improves CRC statistics handling for pyMC modem transports:

• pymc_usb
• pymc_tcp

The repeater now treats modem CRC counts as device-owned cumulative counters and baselines the first observed value rather than recording it as a startup CRC spike.

Existing CRC behavior remains unchanged for:

• sx1262
• sx1262_ch341
• kiss

Configuration Updates

Updated config.yaml.example to document:

• gps.source: modem_http
• Modem HTTP GPS configuration
• Generic pymc_modem sensor configuration examples

Files Changed

• config.yaml.example
• repeater/config.py
• repeater/data_acquisition/gps_service.py
• repeater/engine.py
• repeater/sensors/pymc_modem.py
• tests/test_engine.py
• tests/test_gps_service.py
• tests/test_sensors.py

Validation

Targeted test suite:

.venv/bin/python -m pytest \
  tests/test_gps_service.py \
  tests/test_sensors.py \
  tests/test_engine.py -q

Result:

359 passed in 2.35s

Additional coverage added for:

• Modem HTTP GPS ingestion
• Satellite detail preservation
• Satellite SNR summary generation
• pymc_modem sensor operation
• Missing-coordinate modem payloads
• CRC counter baselining
• Existing non-pyMC CRC behavior

Operational Verification

Verified on a live repeater deployment:

• Service restarted successfully.
• Modem HTTP GPS ingestion functioning.
• GPS fix status preserved.
• Satellite visibility records stored correctly.
• Azimuth, elevation, and SNR values available for UI plotting.
• Satellite SNR summary generated correctly.

Observed live modem data:

State: valid_fix
Fix: true
Satellites used: 19
Satellites in view: 7
Plottable satellites: 7
SNR summary: present

Backwards Compatibility

• Existing serial GPS sources remain supported.
• Existing file GPS sources remain supported.
• Existing non-pyMC radio CRC behavior is unchanged.
• The pymc_modem sensor is additive.
• The modem_http GPS source is opt-in via configuration.
• Payload normalization tolerates missing GPS and telemetry fields.

Why This Matters

Before this change, pyMC modem deployments could expose a valid GPS fix and satellite counts while losing detailed GSV-style satellite visibility data during ingestion. As a result, the GPS diagnostics UI could show zero plotted satellites despite the modem having complete azimuth, elevation, and SNR information.

This PR preserves and normalizes those satellite records end-to-end, allowing the repeater UI to display the same GPS diagnostic detail available on the modem itself.

[yellowcooln]

pyMC_Modem now has this in the firmware.