chore: fix docs

Author: navaronbracke

lib/src/enums/mobile_scanner_error_code.dart

@@ -27,6 +27,7 @@ enum MobileScannerErrorCode {
   /// Scanning is unsupported on the current device.
   unsupported;
 
+  /// Get the human-readable message for the error code.
   String get message {
     switch (this) {
       case MobileScannerErrorCode.controllerUninitialized:

lib/src/objects/scanner_error_widget.dart

@@ -1,10 +1,17 @@
+/// @docImport 'package:mobile_scanner/src/mobile_scanner.dart';
+library;
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
-import 'package:mobile_scanner/mobile_scanner.dart';
+import 'package:mobile_scanner/src/enums/mobile_scanner_error_code.dart';
+import 'package:mobile_scanner/src/mobile_scanner_exception.dart';
 
+/// This widget represents the default error widget for the [MobileScanner] widget.
 class ScannerErrorWidget extends StatelessWidget {
+  /// Creates a new [ScannerErrorWidget] for the given [error].
   const ScannerErrorWidget({super.key, required this.error});
 
+  /// The error that occurred.
   final MobileScannerException error;
 
   @override