Delete ate.scheduler.eligible_workers from resume path #1802

Decision

Delete ate.scheduler.eligible_workers. A log at the rejection answers the question better and costs nothing on the success path.

Why

It is expensive on the resume path. The metric builds a second slice of matching workers that scheduling never reads, walks it again, and repeats the room check for each entry. That check parses resource quantity strings up to three times for each worker. The metric roughly doubles the per-worker arithmetic of a placement.

A metric cannot answer the question it was built for. #564 wanted to tell a full fleet apart from an empty constraint intersection, such as a cordoned node behind a node requirement. That needs the selector, the node requirement and the actor. substrate.yaml forbids those as metric labels and says to put them on logs and spans.