Support for proof generation in rust

This lib lacks support for generating proofs in rust, which will be required in order to generate ibc packet proofs from a substrate runtime

Start by reviewing the repository's existing merkle proof interfaces and Rust support to determine where proof generation belongs. Define the required proof output for IBC packet proofs from a Substrate runtime, then verify that the implementation can generate valid proofs for that use case.

Written by the indexing model from the issue text.