docs: expand example to show valid/invalid cases and optional parameters

Previously the example showed a single email validation with no context.
The new example demonstrates:
- Valid and invalid email cases with explanations
- allowTopLevelDomains (intranet/localhost addresses)
- allowInternational flag in both directions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

example/example.dart

@@ -1,8 +1,37 @@
 import 'package:email_validator/email_validator.dart';
 
 void main() {
-  const String email = 'fredrik.eilertsen@gail.com';
-  final bool isValid = EmailValidator.validate(email);
+  // Basic validation — default: allowTopLevelDomains=false, allowInternational=true
+  final examples = [
+    ('user@example.com', 'standard address'),
+    ('invalid-email', 'missing @'),
+    ('user@', 'missing domain'),
+    ('" "@example.org', 'quoted space — valid per RFC'),
+  ];
 
-  print('Email is valid? ${isValid ? 'yes' : 'no'}');
+  print('--- Basic validation ---');
+  for (final (email, note) in examples) {
+    final valid = EmailValidator.validate(email);
+    print('  ${valid ? '✓' : '✗'} $email  ($note)');
+  }
+
+  // Allow top-level domains (useful for intranet/localhost addresses)
+  print('\n--- allowTopLevelDomains = true ---');
+  for (final email in ['admin@localhost', 'user@intranet']) {
+    final valid = EmailValidator.validate(email, true);
+    print('  ${valid ? '✓' : '✗'} $email');
+  }
+
+  // International addresses (enabled by default)
+  print('\n--- International addresses (default: allowed) ---');
+  final international = [
+    '伊昭傑@郵件.商務', // Chinese
+    'θσερ@εχαμπλε.ψομ', // Greek
+  ];
+  for (final email in international) {
+    final validOn = EmailValidator.validate(email); // allowInternational=true
+    final validOff =
+        EmailValidator.validate(email, false, false); // allowInternational=false
+    print('  allowed=$validOn  rejected=${!validOff}  $email');
+  }
 }