The role of input visualizers

[Matistjati]

We currently say

problem-package-format/spec/2025-09.md

Line 394 in fb3e378

The `validation_time`, `validation_memory`, and `validation_output` limits also apply to input visualizers and output visualizers.

But don't define when they are run. Should this be part of the spec? Maybe it should, as we do define their command-line "signature" and provide input_visualizer_args.