* [Swift] Verify size-prefixed roots from reader position
Validate the size prefix before advancing ByteBuffer.reader, then use the active reader position consistently for root, file identifier, and returned-object verification. Cover malformed decoy roots, oversized prefixes, short identifiers, and valid prefixed identifiers.
* Use wrapping arithmetic in Swift verifier
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Co-authored-by: Darren Carreras <283775510+carrerasdarren-cell@users.noreply.github.com>
