isBic function
Returns true if the BIC/SWIFT code is valid
Implementation
bool isBic(String? value) {
if (value == null || value.isEmpty) return false;
// Remove spaces and convert to uppercase
final cleaned = value.replaceAll(RegExp(r'\s'), '').toUpperCase();
// BIC should be either 8 or 11 characters
if (cleaned.length != 8 && cleaned.length != 11) return false;
return _bicRegex.hasMatch(cleaned);
}