Moving FileAccessMode from "file_access_mode.dart" to "options.dart"

Remove [FileAccessModeExtension]

dio/lib/dio.dart

@@ -9,7 +9,6 @@ export 'src/adapter.dart';
 export 'src/cancel_token.dart';
 export 'src/dio.dart';
 export 'src/dio_exception.dart';
-export 'src/file_access_mode.dart';
 export 'src/dio_mixin.dart' hide InterceptorState, InterceptorResultType;
 export 'src/form_data.dart';
 export 'src/headers.dart';

dio/lib/src/dio.dart

@@ -5,7 +5,6 @@ import 'cancel_token.dart';
 import 'dio/dio_for_native.dart'
     if (dart.library.js_interop) 'dio/dio_for_browser.dart'
     if (dart.library.html) 'dio/dio_for_browser.dart';
-import 'file_access_mode.dart';
 import 'dio_mixin.dart';
 import 'headers.dart';
 import 'options.dart';

dio/lib/src/dio/dio_for_native.dart

@@ -6,7 +6,6 @@ import '../adapters/io_adapter.dart';
 import '../cancel_token.dart';
 import '../dio.dart';
 import '../dio_exception.dart';
-import '../file_access_mode.dart';
 import '../dio_mixin.dart';
 import '../headers.dart';
 import '../options.dart';
@@ -98,10 +97,9 @@ class DioForNative with DioMixin implements Dio {
     // because it can write all bytes by once. Consider that the file is
     // a very big size (up to 1 Gigabytes), it will be expensive in memory.
     RandomAccessFile raf = file.openSync(
-      mode: fileAccessMode.map(
-        write: () => FileMode.write,
-        append: () => FileMode.append,
-      ),
+      mode: fileAccessMode == FileAccessMode.write
+          ? FileMode.write
+          : FileMode.append,
     );
 
     // Create a Completer to notify the success/error state.

dio/lib/src/dio_mixin.dart

@@ -11,7 +11,6 @@ import 'adapter.dart';
 import 'cancel_token.dart';
 import 'dio.dart';
 import 'dio_exception.dart';
-import 'file_access_mode.dart';
 import 'form_data.dart';
 import 'headers.dart';
 import 'interceptors/imply_content_type.dart';

dio/lib/src/options.dart

@@ -753,3 +753,17 @@ class _RequestConfig {
   ResponseDecoder? responseDecoder;
   late ListFormat listFormat;
 }
+
+/// {@template dio.options.FileAccessMode}
+/// The file access mode when downloading a file, corresponds to a subset of
+/// dart:io::[FileMode].
+/// {@endtemplate}
+enum FileAccessMode {
+  /// Mode for opening a file for reading and writing. The file is overwritten
+  /// if it already exists. The file is created if it does not already exist.
+  write,
+
+  /// Mode for opening a file for reading and writing to the end of it.
+  /// The file is created if it does not already exist.
+  append,
+}