Optimize PUSH (#627)

GCC misses the optimization in the original code (uses a temporary storage for `r`). The reworked version fixes this.

GCC 12 regression: 
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109667 
- https://godbolt.org/z/avM74o3r6

lib/evmone/instructions.hpp

@@ -811,7 +811,9 @@ inline code_iterator push(StackTop stack, ExecutionState& /*state*/, code_iterat
     constexpr auto num_full_words = Len / sizeof(uint64_t);
     constexpr auto num_partial_bytes = Len % sizeof(uint64_t);
     auto data = pos + 1;
-    uint256 r;
+
+    stack.push(0);
+    auto& r = stack.top();
 
     // Load top partial word.
     if constexpr (num_partial_bytes != 0)
@@ -827,7 +829,6 @@ inline code_iterator push(StackTop stack, ExecutionState& /*state*/, code_iterat
         data += sizeof(uint64_t);
     }
 
-    stack.push(r);
     return pos + (Len + 1);
 }