Fix #2 Preserve unsigned 64-bit decoded values

tests/README.md

@@ -22,6 +22,7 @@ The executable returns a nonzero exit code if any case fails. Checks remain
 active in release builds and do not depend on `assert` or an external test framework.
 
 Coverage includes Motorola bit numbering within and across bytes, unaligned
-signals, signed values, scaling, 64-bit extraction, invalid lengths, insufficient
+signals, signed values, scaling, 64-bit extraction, signed/unsigned boundary values
+(including `INT64_MIN`, `INT64_MAX`, and `UINT64_MAX`), numeric output, invalid lengths, insufficient
 payloads, and Intel regression cases. Frame validity means the definition was
 found; insufficient payloads are checked through signal validity.