feat: correct serialize of "bytes" data format

main.go

@@ -15,6 +15,7 @@ func FileUploadRoute(req *server.Request) *server.Response {
 	log.Println("[MAIN] File Upload request:", req)
 	bytes, err := req.ExtractBytes()
 	if err != nil {
+		log.Fatalln("Failed to extract bytes from payload:", err)
 		return server.NewStatusResponse(server.STATUS_INTERNALERR)
 	}
 

received.bin

@@ -1,2 +0,0 @@
-Hello, everyone!
-I'm a txt file

server/response.go

@@ -62,7 +62,11 @@ func (res *Response) ToPacket() *Packet {
 
 	maps.Copy(headers, res.Headers)
 
+	if res.Format.Format == DF_BYTES {
+		headers[H_DATA_FORMAT] = DF_BYTES
+	} else {
 		headers[H_DATA_FORMAT] = fmt.Sprintf("%s:%s", res.Format.Format, res.Format.Encoding)
+	}
 	headers[H_STATUS] = strconv.Itoa(res.StatusCode)
 
 	return BuildPacket(headers, res.Payload)
@@ -87,4 +91,3 @@ func (res *Response) Write(p []byte) (int, error) {
 
 	return n, err
 }
-