Function apply_to_node 

pub fn apply_to_node(
    node: &mut Node,
    defs: &BTreeMap<String, MetricDef>,
    engine: &Engine,
)

Apply the node-scope engine to one node: read its numeric attributes, compute every registry metric, and write the results back, omitting each at its omit_at exactly like crate::write_metrics. Built-in attributes already present are used as inputs.