Add AS3935 lightning sensor telemetry fields

[ndoo]

What does this PR do?

Adds the schema needed to support an AS3935 lightning-detection sensor in meshtastic/firmware (companion firmware PR: meshtastic/firmware#10931, branch feat/as3935-lightning-sensor on mesh-malaysia/meshtastic-firmware).

In meshtastic/telemetry.proto:

• EnvironmentMetrics.lightning_strike_count_1h (uint32, field 24) — lightning strikes detected in the last hour, matching the rainfall_1h naming convention.
• EnvironmentMetrics.lightning_distance_km (float, field 25) — estimated distance to the leading edge of the storm for the most recently detected strike in the current window, valid only when a genuine strike (not noise/disturber) was classified.
• TelemetrySensorType.AS3935 (enum value 55).

Field numbers were the next free slots in both EnvironmentMetrics (last used: 23, one_wire_temperature) and TelemetrySensorType (last used: 54, SPA06).

Related Issue

Checklist before merging

• All top level messages commented
• All enum members have unique descriptions

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Note: this repo's develop branch (not master) is what meshtastic/firmware's own develop branch submodule-pins to — this PR targets develop accordingly.

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