Rust Integration: Full Rust Integration

[ohjuny]

This PR follows #1 . (And replaces #2 )
#1 : Sets up pyo3 integration and replaces calls to nx.maximum_flow with a Rust implementation.
In particular, #1 constructs and destructs a Rust-side PhillipsDessouky object every iteration, and therefore incurs interop overhead at every iteration.

This PR seeks to replace all (or most of) solver.py such that all the iterations can be performed in Rust without having to go back to Python.

TODO: more information

[ohjuny]

(just noting down some things for myself)

Cost Model Issues
CostModel in Python is abstract base class - in Rust this is a trait. Operations have a cost model, which is generic over this trait. But pyo3 doesn't support passing in trait-bound objects. There are workarounds, in particular using Box<dyn ModelCost> where ModelCost is the trait - CostModel contains a dyn Box to ExponentialModel. But this makes the CostModel constructor weird, in that it needs to take in a dynamic type, which pyo3 doesn't support.

• Summary Doc: https://docs.google.com/document/d/1HwbvBKhANBGl3dqMQBkt3siUz9hYkipNH9atkt5IooA/
• Generic Classes: Question: How can I pass generic cutom classes to a method PyO3/pyo3#696
• Boxed Input: [Python] Support recursive shapes that are boxed in Rust smithy-lang/smithy-rs#2476
• Box in new: https://stackoverflow.com/questions/75159336/using-box-with-pyo3
• pyo3 trait bound function: https://pyo3.rs/main/trait-bounds
• Trait-bound input: https://stackoverflow.com/questions/77707102/how-to-use-a-trait-as-parameter-of-pymethod-in-pyo3