feat: don't require model file for verifier

[alexander-camuto]

Recent updates in #208 mean that ModelCircuit can be configured using a params object. Here we serialize this object and pass it to verifying functions such that the verifier no longer requires a model onnx file : )

verify commands just require a --circuit-params-path flag pointing to a serialized ModelParams struct, which holds the following information:

/// model parameters
#[derive(Clone, Debug, Default, Serialize, Deserialize)]
pub struct ModelParams {
    /// run args
    pub run_args: RunArgs,
    /// the visibility of the variables in the circuit
    pub visibility: VarVisibility,
    /// the potential number of constraints in the circuit
    pub num_constraints: usize,
    /// the shape of public inputs to the circuit (in order of appearance)
    pub instance_shapes: Vec<Vec<usize>>,
    /// required_lookups
    pub required_lookups: Vec<LookupOp>,
}