pub fn latest_version(&self) -> anyhow::Result<Option<u64>> {
        let Some(manifest) = self.db.try_manifest()? else {
            return Ok(None);
        };
        Ok(manifest.version_count.checked_sub(1))
    }
Returns the latest version of the tree present in the database, or `None` if
no versions are present yet.
core/lib/zk_os_merkle_tree/src/lib.rs