class Watch

Change notification for battery state using a hanging-get pattern.

The first call returns the full current hardware state immediately. Subsequent calls block

until a state change matches the masks in [`ConfigureWatch`]. Each return contains a

complete telemetry snapshot of all current battery fields, not a sparse delta.

At most one `Watch` call may be outstanding per connection; concurrent calls fail with

`ALREADY_WATCHING`.

Parameters:

+ `lease`: An optional power lease token used to coordinate handoff between client and

server, preventing the system from suspending before critical battery events are handled.

If omitted, no lease coordination is performed. If the driver advertises no `wake_on`

fields in `Spec.supported_options`, `lease` is ignored and `wake_lease` is always omitted.

Returns:

+ `status`: Complete current telemetry snapshot of the battery.

+ `wake_lease`: An optional lease token provided if the change triggered a `wake_on`

condition.

Omitted if the change did not trigger a wake condition or if suspend coordination is

inactive.

Errors:

- `ALREADY_WATCHING`: A `Watch` call is already pending on this connection.

- `IO`: Communication failure with the fuel gauge hardware (e.g. I2C transfer failure).

- `INTERNAL`: Internal driver error.