CacheManager attempts to create file named guid.* on Windows (full example included and clear description)

## 🐛 Bug Report

While downloading an image from a webserver the cache manager decides to create a filename ending with .* which is not permitted on windows.

### Expected behavior

Create a filename without extension or a generic extension like .cache or .file since the cache manager cannot determine it from the webserver headers.

### Reproduction steps

i have made minimal reproducible example no external dependencies needed (other than http package)
i am aware that the server should provide correct descriptive headers for the content being served but sometimes it happens not to in some scenarios.

```
import 'package:flutter_cache_manager/flutter_cache_manager.dart';
import 'package:http/http.dart' as http;
import 'package:http/testing.dart';

Future main() async {
final client = MockClient((http.Request request) async =>
http.Response("a png image", 200, headers: {
"content-type": "application/*",
"content-disposition":
"attachment; filename=file; filename*=UTF-8''file"
}));

final cmgr = CacheManager(Config(DefaultCacheManager.key,
fileService: HttpFileService(httpClient: client)));

/* crashes with
Launching lib\main.dart on Windows in debug mode...
√ Built build\windows\runner\Debug\cache_mgr_test.exe.
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: FileSystemException: Cannot open file, path = 'C:\Users\csman\AppData\Local\Temp\libCachedImageData\cf09f070-6cef-1d8a-b096-2334712b3134.*' (OS Error: The filename, directory name, or volume label syntax is incorrect.

, errno = 123)
#0 _checkForErrorResponse (dart:io/common.dart:55:9)
#1 _File.open. (dart:io/file_impl.dart:381:7)

*/

await cmgr.downloadFile("http://myaddress.com/imageManager?pngfileid=1234");
}

/*
pubspec.yaml

name: cache_mgr_test
description: A new Flutter project.
publish_to: "none"
version: 1.0.0+1
environment:
sdk: ">=3.1.5 <4.0.0"
dependencies:
cupertino_icons: ^1.0.2
flutter:
sdk: flutter
flutter_cache_manager: ^3.3.1
http: ^1.1.0
dev_dependencies:
flutter_lints: ^2.0.0
flutter_test:
sdk: flutter
flutter:
uses-material-design: true
*/

```

### Configuration

**Version:** 3.3.1

**Platform:**
Windows 10

I think the problematic part is in \flutter_cache_manager-3.3.1\lib\src\web\file_service.dart line 115 around
```
@override
String get fileExtension {
var fileExtension = '';
final contentTypeHeader = _header(HttpHeaders.contentTypeHeader);
if (contentTypeHeader != null) {
final contentType = ContentType.parse(contentTypeHeader);
fileExtension = contentType.fileExtension;
}
return fileExtension;
}
```

疑わしいロジックは lib/src/web/file_service.dart の 115 行目付近にあります。まず、提供されている最小再現を Windows で実行し、content-type ヘッダーがキャッシュのファイル名の拡張子になるまでの流れを追跡してください。ヘッダーに使用可能な拡張子がないダウンロードで Windows で有効なファイル名が作成され、通常の拡張子が引き続き機能すれば完了です。

索引モデルが issue の本文から書いたものです。