Function HasC2PAManifest

Inspects an ISO-BMFF (MP4/MOV) buffer's top-level boxes for a C2PA JUMBF uuid manifest box.

Walks top-level [size: u32 BE][type: 4 ASCII] boxes:

• size === 1: reads 64-bit largesize at +8 (header is 16 bytes)
• size === 0: box extends to the end of the buffer (header is 8 bytes)
• Any truncated or invalid box size stops the walk cleanly and returns false.