* Add a test to reproduce #3023. Also applied verilog-mode formatting.
* use unique_ptr. No functional change is intended.
* Introduce restorer that reverts changes during iterate() if failed.
* Tests: Add more case that does not match native C++ width (8, 16, 32 or 64).
* Use AstVarRef::same() instead of AstNode::sameGateTree() because the latter checks dtype in addition to scope.
AstVarRef may have different minWidth in some cases,
but the difference should be ignored in the context of bitOpTree optimization.
