fix: ensure data mutex is unlocked a minimum amount of time

fix occasional crash if the receive loop blocks the data mutex for most of the time. the gui loop nearly never gets its chance to block the mutex, especially on slower machines. this should be revesited to ensure no mutex related crashes can happen.

src/DataHandler.cpp

@@ -25,7 +25,7 @@ void DataHandler::receiver_loop()
         sparq_message_t message = receive_message();
         if (message.valid)
         {
-            std::lock_guard<std::mutex> lock(_data_mutex);
+            std::unique_lock<std::mutex> lock(_data_mutex);
 
             if (message.message_type == sparq_message_type_t::STRING)
             {
@@ -35,7 +35,11 @@ void DataHandler::receiver_loop()
             {
                 add_to_datasets(message);
             }
+
+            lock.unlock();
         }
+
+        std::this_thread::sleep_for(500us);
     }
 }