uid property
The tag's 64-bit UID, in the little-endian order it arrived in -- the reverse of Iso15693.icSerialNumber, so the two do not compare byte for byte.
Only Iso15693.getSystemInfoAndUid fills this in; the deprecated Iso15693.getSystemInfo calls a selector that never reported one. Null too when the tag answered without it.
Implementation
final Uint8List? uid;