Constant WILDCOPY_OVERLENGTH 

pub const WILDCOPY_OVERLENGTH: usize = crate::decoding::buffer_backend::WILDCOPY_OVERLENGTH; // 16usize

SIMD wildcopy overshoot slack carried by every decoder backend. Mirrors donor zstd’s WILDCOPY_OVERLENGTH (16 bytes). Public so callers sizing an output slice for crate::decoding::FrameDecoder::decode_to_slice_trusted can size frame_content_size + WILDCOPY_OVERLENGTH without duplicating the constant.