checkValidGSTNumber static method
Check if string is a valid GST number (Indian GST format)
gstNumber - The GST number to validate
Returns true if GST number is valid
Implementation
static bool checkValidGSTNumber(String gstNumber) {
// GST format: 2 digits, 2 letters, 4 digits, 1 letter, 1 digit, 1 letter, 1 digit (e.g., 22ABCDE1234F1Z5)
final gstRegex = RegExp(r'^[0-9]{2}[A-Z]{2}[0-9]{4}[A-Z]{1}[0-9]{1}[A-Z]{1}[0-9]{1}$');
return gstRegex.hasMatch(gstNumber.toUpperCase());
}