Add ChronoFormatter to serialize

src/serialize.h

@@ -520,6 +520,29 @@ struct CompactSizeFormatter
     }
 };
 
+template <typename U, bool LOSSY = false>
+struct ChronoFormatter {
+    template <typename Stream, typename Tp>
+    void Unser(Stream& s, Tp& tp)
+    {
+        U u;
+        s >> u;
+        // Lossy deserialization does not make sense, so force Wnarrowing
+        tp = Tp{typename Tp::duration{typename Tp::duration::rep{u}}};
+    }
+    template <typename Stream, typename Tp>
+    void Ser(Stream& s, Tp tp)
+    {
+        if constexpr (LOSSY) {
+            s << U(tp.time_since_epoch().count());
+        } else {
+            s << U{tp.time_since_epoch().count()};
+        }
+    }
+};
+template <typename U>
+using LossyChronoFormatter = ChronoFormatter<U, true>;
+
 class CompactSizeWriter
 {
 protected: