feat(tree): handle no-op updates in trie update differences

[shekhirin]

Several changes:

1. Do not consider no-op updates (same value as in the database, or deletion of a non-existent key) as a difference.
2. Compare non-existent storage trie updates as empty. It means that if hash builder does a no-op update of a portion of a storage trie, but sparse trie doesn't update it at all, we will compare the hash builder updates to a list of empty updates from sparse trie.
3. Log trie update differences as WARN logs, so that you can see them in stdout without looking into the file. This should now be a sign of malfunction, because we don't expect to have any logs about differences. It will not affect regular users, because the whole trie updates comparison functionality is behind the --engine.state-root-task-compare-updates flag.