add trellis.2 backend back 3d model generation

[eyecreate]

Is your feature request related to a problem? Please describe.

There is no support for trellis backend, which allows generating 3d model content.

Describe the solution you'd like

A maintained backend using GGML exists here: https://github.com/pwilkin/trellis.cpp

Describe alternatives you've considered

Additional context

[localai-org-maint-bot]

I’m picking this up. I’ll inspect the previous TRELLIS integration and current backend conventions, then restore 3D generation using the maintained trellis.cpp implementation with focused tests and documentation.