- Add _strip_region_prefix() to handle us./eu./apac./global. prefixes
- Update get_context_window_size() with V4 model entries (200K tokens)
- Update supports_multimodal() to detect V4 models
- Update _is_nova_model() to use region prefix stripping
- Add V4 model context windows to LLM_CONTEXT_WINDOW_SIZES in llm.py
- Add 11 comprehensive tests covering V4 model detection, context windows,
multimodal support, region prefixes, function calling, and regression
Closes#4700
Co-Authored-By: João <joao@crewai.com>