Constant MAX_XMP_LENGTH 

pub const MAX_XMP_LENGTH: usize = _; // 16_777_216usize

Upper bound on XMP packet length accepted by parse_xmp. Guards against CPU exhaustion on crafted inputs.

Matches ultrahdr_core::limits::MAX_XMP_LENGTH (the pre-migration value) so callers moving between the old and new API see no change in accepted input size. Legitimate gain-map XMP is well under 32 KB, but Extended XMP reassembly + base64-encoded depth-map payloads (GDepth / Android Dynamic Depth) can push into MB range, so a generous cap is appropriate.