using simpletuner's AGPL3 code for quantisation

Hello, it's not a super big deal, but I noticed that the quantisation helpers used by ltx-trainer package are from SimpleTuner, which is AGPLv3. This repo is incompatibly licensed. You would have to relicense this repo under AGPLv3 to become compatible.

You could replace that code with your own. In general, it's not advised to lift code from open-source projects without attribution or correct licensing.