feat: `CommitmentScheme` trait + example

[Autoparallel]

Idea

We currently have no examples of CommitmentSchemes in our crate! This cannot be! So, we should implement a standard trait that any and all commitment schemes should use and provide some examples.

Examples

• Hash based commitment scheme (should be quick to implement!)
• Pedersen commitment
• Polynomial commitment (e.g., KZG)
• Vector commitment (e.g., Merkle tree)

Of the above, hash and vector could be done with what we already have. Implementing Pedersen and KZG would be of interest to more of the ZK community, surely.

[RajeshRk18]

I will work on this!

[Autoparallel]

You got it @RajeshRk18

[devloper]

We have univariate KZG! I'd love to see more. Code-based commitment schemes, multivariate kzg and others