feat(p2p): Allow overriding the p2p udp port for Minecraft

the idea is that you might port forward this in your router and give yourself NAT type A for free

src/utils/scope_exit.h

@@ -0,0 +1,13 @@
+#pragma once
+#include <functional>
+
+// https://stackoverflow.com/a/61242721
+template<typename F>
+struct scope_exit
+{
+    F func;
+    explicit scope_exit(F&& f): func(std::forward<F>(f)) {}
+    ~scope_exit() { func(); }
+};
+
+template<typename F> scope_exit(F&& frv) -> scope_exit<F>;