trie, core/state: revert error removal in (*state.Trie).Commit

[gballet]

This has been discussed with @rjl493456442 : the error result was removed from (*state.Trie).Commit as no error could occur in the MPT's Commit function. In verkle, however, errors can happen and should be reported.

[fjl]

What kind of errors can happen in the verkle tree during commit?

[rjl493456442]

I would prefer to reform the code like

root, nodes, err := tr.Commit(false)
if err != nil {
    return nil, err
}
s.data.Root = root
return nodes, nil

[rjl493456442]

I have nothing to against, if verkle needs to return error.

Only a nitpick, lgtm.

[gballet]

What kind of errors can happen in the verkle tree during commit?

Looking at the code:

• invalid root node type if the deserialization didn't work properly
• an error occuring during the batch-serialization of a node
• error writing the serialized nodes to disk (although this would no longer happen once PBSS becomes verkle-friendly)

None of that should happen in practice, but if it does it'd be vital to capture that error.

[rjl493456442]

Yeah, in MPT, (2) node encoding will never fail since we always write to a local buffer and (3) we won't do any database write even in current master in commit function.

But I think it's ok to return an error. Error might occurs in verkle, e.g. some cryptography operations.