Function run 

pub fn run(
    src: &str,
    node_id: Option<&str>,
    json: bool,
) -> Result<String, InspectCmdErr>

Run zenith inspect.

• src — raw .zen source text.
• node_id — when Some, restrict output to the subtree rooted at that id.
• json — emit JSON instead of the human-readable tree.

Returns a formatted string on success, or an InspectCmdErr on parse error, not-found error, etc.