- Add __getstate__/__setstate__ to drop cached _compiled Jinja2 template
- Jinja2 Template.root_render_func is a dynamic closure unpicklable by reference
- cached_property rebuilds the template lazily on first render after unpickle
- ChatTemplate: defer Jinja2 compilation to cached_property, exclude compiled template from __getstate__ (its dynamic root function has __module__=None and falls back to __main__, breaking pickle)
- AutoTokenizer: bypass __getattr__ for underscore-prefixed attrs to prevent infinite recursion during unpickle when __dict__ is empty