Apply suggestions from code review

packages/stream_chat/lib/src/core/api/attachment_file_uploader.dart

@@ -16,7 +16,7 @@ abstract class AttachmentFileUploader {
     String channelType, {
     ProgressCallback? onSendProgress,
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   });
 
   /// Uploads a [file] to the given channel.
@@ -30,7 +30,7 @@ abstract class AttachmentFileUploader {
     String channelType, {
     ProgressCallback? onSendProgress,
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   });
 
   /// Deletes a image using its [url] from the given channel.
@@ -42,7 +42,7 @@ abstract class AttachmentFileUploader {
     String channelId,
     String channelType, {
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   });
 
   /// Deletes a file using its [url] from the given channel.
@@ -54,7 +54,7 @@ abstract class AttachmentFileUploader {
     String channelId,
     String channelType, {
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   });
 }
 
@@ -72,7 +72,7 @@ class StreamAttachmentFileUploader implements AttachmentFileUploader {
     String channelType, {
     ProgressCallback? onSendProgress,
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   }) async {
     final multiPartFile = await file.toMultipartFile();
     final response = await _client.postFile(
@@ -91,7 +91,7 @@ class StreamAttachmentFileUploader implements AttachmentFileUploader {
     String channelType, {
     ProgressCallback? onSendProgress,
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   }) async {
     final multiPartFile = await file.toMultipartFile();
     final response = await _client.postFile(
@@ -109,7 +109,7 @@ class StreamAttachmentFileUploader implements AttachmentFileUploader {
     String channelId,
     String channelType, {
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   }) async {
     final response = await _client.delete(
       '/channels/$channelType/$channelId/image',
@@ -125,7 +125,7 @@ class StreamAttachmentFileUploader implements AttachmentFileUploader {
     String channelId,
     String channelType, {
     CancelToken? cancelToken,
-    Map<dynamic, dynamic>? extraData,
+    Map<String, Object?>? extraData,
   }) async {
     final response = await _client.delete(
       '/channels/$channelType/$channelId/file',