wan 2.2: add AnimeGen T2V model flavour

[bghira]

This pull request adds support for two new AnimeGen T2V model flavors ("animegen-t2v-high" and "animegen-t2v-low") to the Wan model, enabling single-file checkpoint loading for these variants. It also updates the configuration and pipeline logic to handle these new flavors and provides corresponding tests to ensure correct integration.

AnimeGen T2V Model Integration:

• Added "animegen-t2v-high" and "animegen-t2v-low" as available model flavors in model_metadata.json and in the HUGGINGFACE_PATHS mapping in wan/model.py. [1] [2]
• Defined new configuration entries for the AnimeGen flavors, including URLs to their single-file .safetensors checkpoints and associated parameters (e.g., flow shift, sample steps, guidance, etc.). [1] [2]

Model Loading and Pipeline Logic:

• Updated the model setup and pipeline loading logic to handle single-file checkpoints for the AnimeGen flavors, including changes to _get_or_load_wan_stage_module to support both subfolder and single-file loading and to use a more robust cache key. [1] [2] [3]
• Ensured that the correct transformer model path is set during model flavor setup for these new variants.

Testing:

• Added new unit tests to verify that the AnimeGen T2V flavors are correctly recognized, configured, and loaded, and that their parameters are set as expected. [1] [2]

Other:

• Minor adjustment to the validation inference steps warning logic to avoid unnecessary warnings when stage info is present.