Function check_decode_prefix_cases 

pub fn check_decode_prefix_cases<D: DecoderConfig + 'static>(
    decoder: D,
    bytes: &[u8],
    cases: &[PrefixCase<'_>],
) -> Conformance

Exercise explicit complete-payload/truncation boundaries through one-shot and sink dispatch. Successful recovery must produce the expected pixels. The caller supplies strict/compatibility configuration separately. No prefix is silently omitted; out-of-range fixture boundaries are errors.