security(twdata): Zeroize every TWData instance in TWDataDelete, and other TWData improvements

src/interface/TWData.cpp

@@ -4,6 +4,7 @@
 
 #include <TrustWalletCore/TWData.h>
 #include <TrustWalletCore/TWString.h>
+#include <TrezorCrypto/memzero.h>
 #include "Data.h"
 #include "HexCoding.h"
 #include <algorithm>
@@ -95,8 +96,12 @@ void TWDataReset(TWData *_Nonnull data) {
 }
 
 void TWDataDelete(TWData *_Nonnull data) {
-    auto* v = reinterpret_cast<const Data*>(data);
-    delete v;
+    auto* vConst = reinterpret_cast<const Data*>(data);
+    // `const_cast` is safe here despite that the pointer to the data is const
+    // but `Data` is not a constant value.
+    auto *v = const_cast<Data*>(vConst);
+    memzero(v->data(), v->size());
+    delete vConst;
 }
 
 bool TWDataEqual(TWData *_Nonnull lhs, TWData *_Nonnull rhs) {