Implement accurate memory accounting for mempool

src/script/script.h

@@ -6,6 +6,7 @@
 #ifndef BITCOIN_SCRIPT_SCRIPT_H
 #define BITCOIN_SCRIPT_SCRIPT_H
 
+#include "memusage.h"
 #include "crypto/common.h"
 
 #include <assert.h>
@@ -607,6 +608,8 @@ public:
         // The default std::vector::clear() does not release memory.
         std::vector<unsigned char>().swap(*this);
     }
+
+    size_t DynamicMemoryUsage() const;
 };
 
 class CReserveScript