feat: add LAFVIN UPS Module 3S sensor plugin (lafvin_ups_3s)

[CarlsonCustoms]

Summary

• Adds lafvin_ups_3s sensor type for the LAFVIN UPS Module 3S — an INA219-based UPS HAT for Raspberry Pi with a 3S Li-ion/LiPo battery pack
• Reports pack voltage, current, power, estimated state-of-charge (0–100%), and charge state (charging / discharging / idle)
• SoC uses a piecewise linear per-cell curve (pack voltage ÷ 3) consistent with the approach in waveshare_ups_d
• INA219 address defaults to 0x41 (as factory-wired on the LAFVIN board); shunt resistance and max current are configurable for accurate calibration
• Sensor module is auto-loaded by the existing SensorManager import mechanism — no changes to __init__.py or registry required

Config example

sensors:
  definitions:
    - type: lafvin_ups_3s
      name: battery
      enabled: true
      auto_install_packages: false
      settings:
        i2c_address: 0x41
        bus_number: 1
        shunt_ohms: 0.1
        max_amps: 5.0

Test plan

• Confirm i2cdetect -y 1 shows device at 0x41 with LAFVIN UPS connected
• Verify sensor initializes cleanly in repeater log (LAFVIN UPS 3S INA219 initialized)
• Confirm voltage reading matches a multimeter measurement on the pack
• Confirm charge state transitions between charging, discharging, and idle

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