Fix multiproc metrics in no_trainer examples
# Fixes a bug in the `no_trainer` scripts involving metric evaluation

## What does this add?

Fixes up the metric evaluation in most of the `no_trainer` scripts when multi-processing is involved. The final batch gets duplicated in those situations, so the metrics are slightly higher (or lower) than their actual values.

## Who is it for?

Users of the `no_trainer` scripts
_The documentation is not available anymore as the PR was closed or merged._