Function validateC2paSegment

validateC2paSegment(
    segmentBytes: Uint8Array,
    sessionKeys: readonly ValidatedSessionKey[],
    sequenceState?: SequenceState,
): Promise<
    | { nextSequenceState: SequenceState; result: SegmentValidationResult }
    | null,
>
Validates a C2PA live stream segment using the VSI/EMSG method (§19.7.3).

Extracts the EMSG box, decodes the COSE_Sign1 and VSI map, matches the session key by kid, then performs all cryptographic checks: signature verification, BMFF content hash, sequence number floor, and key validity.

Returns null if the segment does not contain a C2PA EMSG box.
Parameters
- segmentBytes: Uint8Array
  Raw segment bytes
- sessionKeys: readonly ValidatedSessionKey[]
  Available session keys from the init segment
- sequenceState: SequenceState = ...
  Current sequence state for this stream
Returns Promise<
| { nextSequenceState: SequenceState; result: SegmentValidationResult }
| null,
>
Validation result and updated sequence state, or null if no C2PA EMSG box
Example
```
it('returns null when segment has no C2PA EMSG box', async () => {
	const result = await validateC2paSegment(
		new Uint8Array(0),
		[],
	)

	strictEqual(result, null)
})
```
- Defined in segment/validateC2paSegment.ts:39