GUISlice support

**Describe the problem you have/What new integration you would like**
Support for GUISlice, a development package similar to nextion, but open source.

**Please describe your use case for this integration and alternatives you've tried:**
no particular need apart from the fact nextion can be awful with support, and this is an open source alternative.

**Additional context**
https://github.com/ImpulseAdventure/GUIslice

Review the linked GUIslice project and compare its integration requirements with ESPHome's existing project structure. The issue names no ESPHome files, tests, entry points, or acceptance criteria, so first define the supported scope and how completion will be verified.

Written by the indexing model from the issue text.