A Cross Platform UUID for K/N

K/N doesn't have a UUID yet. This brings a random (v4) UUID that matches UUIDs on various platforms:

• iOS/Mac: NSUUID
• Java: java.util.UUID (specifically randomUUID)

This UUID is:

• Frozen
• Thread-safe (thread-safe randomness in native)
• Adheres to RFC4122 (version 4 UUID)
• Tested
• Tested against macOS/iOS UUID to verify correctness