mempool: apply rule of 5 to epochguard.h, fix compiler warnings

Author: jonatack

src/util/epochguard.h

@@ -40,6 +40,9 @@ class LOCKABLE Epoch
     Epoch() = default;
     Epoch(const Epoch&) = delete;
     Epoch& operator=(const Epoch&) = delete;
+    Epoch(Epoch&&) = delete;
+    Epoch& operator=(Epoch&&) = delete;
+    ~Epoch() = default;
 
     bool guarded() const { return m_guarded; }
 
@@ -51,6 +54,13 @@ class LOCKABLE Epoch
         // only allow modification via Epoch member functions
         friend class Epoch;
         Marker& operator=(const Marker&) = delete;
+
+    public:
+        Marker() = default;
+        Marker(const Marker&) = default;
+        Marker(Marker&&) = delete;
+        Marker& operator=(Marker&&) = delete;
+        ~Marker() = default;
     };
 
     class SCOPED_LOCKABLE Guard