Implement Clone and Debug for internal_scc::SccGraph and Debug for _Edge #147
Description
To implement Clone and Debug for SccGraph and TwoSat, internal_scc::SccGraph must also support Clone and Debug.
Additionally, implementing Debug for internal_scc::SccGraph requires implementing Debug for _Edge.
The Clone trait for internal_scc::SccGraph can be derived.
For the Debug trait, discussion is needed regarding the output format.
I think that the Debug trait for _Edge can simply be derived.
Similarly, I think deriving Debug for internal_scc::SccGraph is also sufficient.