bug(lightclient/groth16): code commitment isn't used or documented

[rootulp]

Context

celestia-zkevm-ibc-demo/testing/demo/pkg/setup/initialise_groth16_client.go

Line 72 in 620a002

clientState := groth16.NewClientState(latestBlock.Number().Uint64(), []byte{}, []byte{}, []byte{}, genesisBlock.Root().Bytes())

Problem

CodeCommitment isn't provided in this invocation. Even worse, there are no docs on what code commitment expects.

Proposal

1. Add a more helpful doc to the CodeCommitment field in client state
2. Populate a CodeCommitment when creating the Groth16 light client.

[rootulp]

It may refer to a commitment of the EVM Prover source code.