Switchable Backends

[Naphann]

Features to be requested:

Right now we only have two backends which are the Error basis model for state simulation and graph state backend for stabilizer simulation. We want to be able to switch backend so we can crosscheck the results.

Necessary backends:

• Density matrices formulation (using Qiskit/Cirq/QuTip or maybe implement one ourselves using Eigen)
• Stim from Craig Gidney's [paper](https://quantum-journal.org/papers/q-2021-07-06-497/ to verify our own graph backends and it should be faster when we simulate error-corrected LAN or 2G repeater networks using large code.
• Improved error basis: it should be completely separated from the RuleEngine and keep be context-aware (maybe as a separate issue)

Things to be done:

Right now we have IStationaryQubit as the interface, need to somehow make this connectable to the external library or at least show an example of one.