Function cast 

pub fn cast(
    encoder: &mut CommandEncoder,
    registry: &mut KernelRegistry,
    device: &DeviceRef,
    input: &MlxBuffer,
    output: &MlxBuffer,
    n_elements: usize,
    direction: CastDirection,
) -> Result<()>

Encode a dtype cast operation.

Errors

Returns MlxError::InvalidArgument if n_elements is zero or buffers are too small.