feat: complete sell

lib/data/services/api_client.dart

@@ -310,6 +310,31 @@ class ApiClient {
     }
   }
 
+  Future<Result<void>> sellBooks(Map<String, double?> books) async {
+    final client = Client();
+    try {
+      final headers = await _getHeaders({"Content-Type": "application/json"});
+      debugPrint("\n\n\n\nMAP: $books\n\n\n\n");
+      final body = jsonEncode(books);
+      debugPrint("\n\n\n\nSENT: $body\n\n\n\n");
+      final response = await client.post(
+        Uri.parse("https://$apiBasePath/book_instance/sell/bulk"),
+        headers: headers,
+        body: body,
+      );
+      if (response.statusCode == 200) {
+        return Result.ok(response.statusCode);
+      } else {
+        throw "Unknown error";
+      }
+    } catch (e) {
+      debugPrint("\n\n\n\nERROR : ${e.toString()}\n\n\n\n");
+      return Result.error(Exception(e));
+    } finally {
+      client.close();
+    }
+  }
+
   Future<Result<BookInstance>> sendBook(
     Book book,
     Owner owner,