refactor: deduplicate IRC parsing (#5678)

src/messages/MessageSimilarity.hpp

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "messages/Message.hpp"
+
+#include <ranges>
+namespace chatterino {
+
+template <std::ranges::bidirectional_range T>
+void setSimilarityFlags(const MessagePtr &message, const T &messages);
+
+}  // namespace chatterino