`tech_library` default copy constructor is not fully copying the class

[dinoruic]

mockturtle::tech_library contains member variables super_utils and struct_library which both contain a reference to _gates. When mockturtle::tech_library is copied, these references will keep pointing to the original location rather than to the new copied location.

The short-term solution is to disable the default copy constructor. Longer-term it would be great to properly implement a copy constructor.

(This is not urgent as we've worked around it).

[aletempiac]

Thank you for reporting! For now, I opted for the short-term solution. If you further suggestions or changes, please feel free to submit a PR at any time.