Function render_indicator 

async fn render_indicator(
    driver: &mut Driver<I2cTransport<I2c<'static, Async, Master>, 2>, 2>,
    state: BacklightState,
) -> Result<(), I2cTransportError<<I2c<'static, Async, Master> as ErrorType>::Error>>

Writes only the Caps Lock indicator LED according to state.

Used when only indicator state has changed and the background is already correct, avoiding a full redraw.

Errors

Returns Err if any bus transaction fails.