Function cast_with_q8_fallback 

pub fn cast_with_q8_fallback(
    data: &[u8],
    src: SrcDtype,
    shape: &[u64],
    out_dtype: GGMLType,
) -> Result<(Vec<u8>, GGMLType, bool)>

Cast with automatic Q8_0 fallback. Returns (bytes, actual_dtype, fell_back).