Function run_plan 

pub fn run_plan<F>(
    plan: Option<&ExecutionPlanSpec>,
    ops: &[OpSpec],
    exec: F,
) -> Result<RunResult, PlanFailure>
where
    F: FnMut(&OpSpec, Option<&Value>) -> ExecOutcome,

Run the plan. exec(op, bound_value) returns the node outcome (mock).