QMP6988 env sensor support

[mokjpn]

Summary

This PR adds environmental telemetry support for the QMP6988 pressure sensor.

Changes included:

• add I2C detection for QMP6988 at 0x70 and 0x56
• add a new QMP6988Sensor telemetry driver
• register QMP6988 in EnvironmentTelemetry
• add the telemetry sensor type for QMP6988
• report temperature and barometric pressure in the same units used by the existing telemetry pipeline

Notes

During testing, some QMP6988 devices did not accept the reset command over this hardware path, but calibration readout and measurements still worked correctly. The driver now treats reset as optional and continues initialization when the sensor is otherwise responsive.

This PR is intended to add QMP6988 support only. It does not address unrelated SHT3x/SHT30 hardware address conflicts on specific boards.

Testing

Tested on:

• Arduino Nesso N1
• M5Stack Unit ENV III connected over Qwiic/Grove adapter

Observed result:

• QMP6988 was detected successfully
• initialization completed successfully
• temperature and barometric pressure telemetry were reported correctly
• pressure scaling was verified and corrected to hPa

Build tested:

• pio run -e m5stack-unitc6l

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)

Other:

• Arduino Nesso N1 + M5Stack Unit ENV III

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[jp-bennett]

Rather than changing protobufs directly here, please make a PR to https://github.com/meshtastic/protobufs with the protobuf changes.

[mokjpn]

Closing this in favor of a split protobufs/firmware flow.

The protobuf enum addition has been moved to a separate PR:

• Add QMP6988 telemetry sensor type protobufs#899

I will reopen the firmware-side change as a clean PR that depends on that protobuf update.