tune: double generator challenge frequency

[dylanuys]

Summary

• reduce the default generator challenge interval from 220 blocks to 110 blocks
• double the generator request cadence without changing validator CLI override behavior

Motivation

We have observed an increase in generator miner registrations. Increasing the request frequency gives the larger generator pool more frequent evaluation coverage and fresher reward data.

Scope

This is intentionally a one-line configuration change. It does not bump the release version.