refactor: use fold expressions instead of recursive calls in UnserializeMany()

Instead of recursively calling `UnserializeMany` and peeling off one
argument at a time, use a fold expression. This simplifies the code,
makes it most likely faster because it reduces the number of function
calls, and compiles faster because there are fewer template
instantiations.

Author: martinus

src/serialize.h

@@ -1045,16 +1045,10 @@ void SerializeMany(Stream& s, const Args&... args)
     (::Serialize(s, args), ...);
 }
 
-template<typename Stream>
-inline void UnserializeMany(Stream& s)
-{
-}
-
-template<typename Stream, typename Arg, typename... Args>
-inline void UnserializeMany(Stream& s, Arg&& arg, Args&&... args)
+template <typename Stream, typename... Args>
+inline void UnserializeMany(Stream& s, Args&&... args)
 {
-    ::Unserialize(s, arg);
-    ::UnserializeMany(s, args...);
+    (::Unserialize(s, args), ...);
 }
 
 template<typename Stream, typename... Args>