Function class_label 

fn class_label(shaper: &Scheduler, class: Class) -> String

The label ProxyEvent::Shaped reports a class under.

An empty string for Class::Default and Class::Unshapeable, matching ShapeStats::default_class and ShapeStats::unshapeable, whose rows are unnamed for the same reason: a user-written class name is unique by ShapeError::DuplicateClassName, so an empty label cannot collide with one and “no rule claimed it” needs no invented name.

Allocates one String, and is called only from an event that is capped at once per stream per outcome — never per unit.