Use a more Rust-friendly type for private inputs

[nalinbhardwaj]

Here we use serde::Value, use something like From<PrimeField> instead and perform the conversion to Circom-friendly JSON in library. This would abstract/simplify lot of the decimal/hex/bytes etc conversions from users of the library:

Nova-Scotia/src/lib.rs

Line 67 in 1bc7e39

private_inputs: Vec<HashMap<String, Value>>,

From https://hackmd.io/80cPXRc0Sa2MPuYX4Wft8w