Reduce proof size using batched Merkle proofs

[andrewmilson]

Batched Merkle proofs allow aggregating multiple Merkle paths into a single proof. The aggregation allows for removing all duplicate internal nodes which significantly decreases the STARK proof size (we're talking 20-40%). Would be great if arkworks or another Rust library could do this (winter-crypto for instance). Implementation in Winterfell: https://github.com/novifinancial/winterfell/blob/main/crypto/src/merkle/proofs.rs#L31

[andrewmilson]

Marking closed. The default merkle tree implementation generates and verifies batched merkle proofs now. This was inspired by the way StarkWare's Ethereum verifier works.