IsoCode.GB incorrectly rejects valid UK mobile numbers

[tyler-jewell]

Description

When constructing a PhoneNumber with IsoCode.GB (Great Britain/United Kingdom) and a valid UK mobile NSN, validation incorrectly returns false. However, the same number validates correctly when using IsoCode.GG (Guernsey).

Steps to Reproduce

import 'package:phone_numbers_parser/phone_numbers_parser.dart';

void main() {
  // UK mobile number: 07911 123456 → NSN is 7911123456
  final gbPhone = PhoneNumber(isoCode: IsoCode.GB, nsn: '7911123456');
  final ggPhone = PhoneNumber(isoCode: IsoCode.GG, nsn: '7911123456');
  
  print('GB: isValid=${gbPhone.isValid()}, isMobile=${gbPhone.isValid(type: PhoneNumberType.mobile)}');
  // Output: GB: isValid=false, isMobile=false
  
  print('GG: isValid=${ggPhone.isValid()}, isMobile=${ggPhone.isValid(type: PhoneNumberType.mobile)}');
  // Output: GG: isValid=true, isMobile=true
}

Additional Observations

1. Parsing auto-detects as Guernsey: PhoneNumber.parse('+447911123456') returns isoCode: IsoCode.GG instead of IsoCode.GB

2. GB landlines work correctly:

final landline = PhoneNumber(isoCode: IsoCode.GB, nsn: '2071234567'); // London
print(landline.isValid(type: PhoneNumberType.fixedLine)); // true

3. Test results summary:

IsoCode	UK Mobile (7911123456)	UK Landline (2071234567)
GB	❌ invalid	✅ valid
GG	✅ valid	❌ invalid

Expected Behavior

PhoneNumber(isoCode: IsoCode.GB, nsn: '7911123456').isValid(type: PhoneNumberType.mobile) should return true for valid UK mobile numbers.

UK mobile numbers start with 7 after the country code (domestic format: 07XXX XXXXXX).

Environment

• phone_numbers_parser: 9.0.18
• Dart SDK: 3.9.0
• Flutter: 3.32.1

Impact

This breaks phone number validation in country picker UIs where users select "United Kingdom" and enter their mobile number. The validation fails even though the number is valid.

Workaround

Currently working around this by using IsoCode.GG for validation when IsoCode.GB is selected and the number starts with 7.

[cedvdb]

https://github.com/cedvdb/phone_numbers_parser/blob/main/resources/data_sources/PhoneNumberMetadata.xml#L11625

Either the metadata is incorrect or the phone is invalid.

Here is why it doesn't match:

• ❌ 9111 does not match 911[028]
• ❌ 911 does not match any allowed 91x pattern in the second branch.