Fix packaging for trio_core.models in built wheel

[simonerom]

Summary

• anchor the .gitignore models/ rule to the repository root
• stop excluding src/trio_core/models from built distributions
• preserve ignoring a top-level models directory for large local artifacts

Problem

A user-installed trio-core package could pass trio doctor and still fail on first MLX inference with:

Missing dependency: No module named 'trio_core.models'

In the installed package, trio_core.models was missing from site-packages.

Root Cause

The repo had this ignore rule:

models/

That pattern also matched src/trio_core/models, which is a runtime Python package. This can cause the build to exclude trio_core.models from the wheel.

I confirmed the match locally with:

git check-ignore --no-index -v src/trio_core/models/__init__.py
# .gitignore:32:models/ src/trio_core/models/__init__.py

Fix

Change the rule to:

/models/

That keeps ignoring only the top-level models directory while allowing src/trio_core/models to be included in the package.

Validation

• confirmed before the change that src/trio_core/models/__init__.py matched .gitignore
• confirmed after the change that it no longer matches
• confirmed a top-level models path is still ignored
• verified the diff is limited to .gitignore

User Impact

This fixes a packaging issue where the published install can be missing runtime MLX model modules, causing inference commands like trio analyze to fail immediately after installation.