wallet: introduce method to return all db created files

src/wallet/test/util.h

@@ -109,6 +109,7 @@ public:
     void Close() override {}
 
     std::string Filename() override { return "mockable"; }
+    std::vector<fs::path> Files() override { return {}; }
     std::string Format() override { return "mock"; }
     std::unique_ptr<DatabaseBatch> MakeBatch() override { return std::make_unique<MockableBatch>(m_records, m_pass); }
 };