docs: move fillRandomBytes example to a separate file

example/webcrypto/random/fill_random_bytes.dart

@@ -0,0 +1,34 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// ignore_for_file: avoid_print
+
+// #region example
+import 'dart:convert' show base64;
+import 'dart:typed_data' show Uint8List;
+
+import 'package:webcrypto/webcrypto.dart';
+
+void main() {
+  // Allocate a byte array of 64 bytes.
+  final bytes = Uint8List(64);
+
+  // Fill with random bytes.
+  fillRandomBytes(bytes);
+
+  // Print base64 encoded random bytes.
+  print(base64.encode(bytes));
+}
+
+// #endregion

lib/src/webcrypto/webcrypto.random.dart

@@ -20,22 +20,7 @@ part of 'webcrypto.dart';
 /// calls to obtain more random bytes.
 ///
 /// **Example**
-/// ```dart
-/// import 'dart:convert' show base64;
-/// import 'dart:typed_data' show Uint8List;
-/// import 'package:webcrypto/webcrypto.dart';
-///
-/// void main() {
-///   // Allocate a byte array of 64 bytes.
-///   final bytes = Uint8List(64);
-///
-///   // Fill with random bytes.
-///   fillRandomBytes(bytes);
-///
-///   // Print base64 encoded random bytes.
-///   print(base64.encode(bytes));
-/// }
-/// ```
+/// {@example /example/webcrypto/random/fill_random_bytes.dart#example}
 void fillRandomBytes(
   TypedData destination,
   // Note: Uint8List and friends all implement TypedData, but dartdoc has a bug