chore: error bubbling

[alexander-camuto]

As we start building out tooling in other languages which calls this core library, we need proper error bubbling ! Note that some of the objectives below can only be partially fulfilled as some halo2 closures / function calls require a returned error of type plonk::Error so can't generically return our custom errors.

• error bubbling up to ezkl main.rs using Box<dyn Error>
• remove asserts and panics!() in /src/tensor and return TensorError which derives thiserror::Error.
• remove asserts and panics!() in /src/circuit and implement CircuitError which derives thiserror::Error (partial).
• remove asserts and panics!() in /src/graph and implement GraphError which derives thiserror::Error (partial)
• remove asserts and panics!() in /src/pfsys and implement PysysError which derives thiserror::Error (partial)