refactor: migrate rust-like ops.

- migrate rust-like ops.
- migrate testbench for them but not finished.

testbench/yycc/num/safe_cast.cpp

@@ -0,0 +1,9 @@
+#include <gtest/gtest.h>
+#include <yycc.hpp>
+#include <yycc/num/safe_cast.hpp>
+
+namespace yycctest::num::safe_cast {
+
+    // TODO: Add testbench
+
+}