Fixed some UBs and memory leaks

1. src/gate/library/cell_gen_utils.cpp: Replaced reverse SubnetBuilderIterator with the forward (bug in reverse SubnetBuillderIterator)
2. src/gate/synthesizer/operation/util_common.cpp: Replaced reverse SubnetBuilderIterator with the forward
3. src/gate/techmapper/estimator/ppa_estimator.h: Replaced reverse SubnetBuilderIterator with the forward
4. src/gate/model/list.h: Added placement new operator to init new elements
5. src/gate/model/subnet/base.h: Added current link deallocation in SubnetCell assignment operators
6. src/gate/model/subnet/builder.cpp: deleted lhs root reference in replace(...) (entries vector can be resized)
7. src/gate/techmapper/subnet_techmapper_base.h: Added virtual destructor in PassConfig
8. src/util/bounded_set.h: added it != container.end() check