isUuid function
Returns true if str is a valid UUID (any version by default).
Pass version as '3', '4', or '5' to match a specific version.
Returns false if str is null.
Implementation
bool isUuid(String? str, [String? version]) {
if (str == null) return false;
final v = version ?? 'all';
final pat = uuidReg[v];
return pat != null && pat.hasMatch(str.toUpperCase());
}