[tullom]

The majority of ECs only have 1 fuel gauge/battery, so it makes more sense to keep that as the default behaviour. Adding the second fuel gauge to demonstrate capability is preserved but in a feature gate.

[Copilot]

🟢 Approval recommended

No active review issues remain for the single-gauge default and opt-in dual-gauge support.

No open issues 🎉

What changed in this PR

This PR makes the shared mock battery service use one fuel gauge by default, while preserving the two-battery demonstration through the opt-in dual-fuel-gauge feature.

Changes:

• Conditionally initialize the second fuel gauge and size registration and task capacity to match.
• Define dual-fuel-gauge in platform-common, enabling mock support.
• Expose the feature through all five platform crates.

File	Description
platform/​platform-common/​src/​mock/​battery.rs	Gate the second gauge and adjust registration and task capacity.
platform/​platform-common/​Cargo.toml	Define the opt-in feature with mock support.
platform/​dev-qemu/​Cargo.toml	Forward the dual-gauge feature to platform-common.
platform/​dev-npcx/​Cargo.toml	Forward the dual-gauge feature to platform-common.
platform/​dev-mec/​Cargo.toml	Forward the dual-gauge feature to platform-common.
platform/​dev-mcxa/​Cargo.toml	Forward the dual-gauge feature to platform-common.
platform/​dev-imxrt/​Cargo.toml	Forward the dual-gauge feature to platform-common.

_{Review effort: Balanced}