Fix ~790 basedpyright errors across the test suite:
- Type stub subclasses of real production classes with super().__init__()
- Add missing generic type arguments and Dict[str, Any] annotations
- Add None guards before subscript/member access
- Adapt tests to production API changes (removed dead handlers,
PersistentModelCache.get_default, _i18n_filter_added location)
Add two new optional parameters to the Save Image node:
- webp_method (INT, 0-6, default 6): Controls WebP compression level.
0=fastest/largest, 6=slowest/smallest. Previously hardcoded to 0.
- jpeg_subsampling (INT, 0-2, default 0): Controls JPEG chroma
subsampling. 0=4:4:4 (best quality), 1=4:2:2, 2=4:2:0.
Frontend JS extension hides/disables each parameter when the
selected file_format doesn't apply (e.g., webp_method is hidden
when saving as PNG or JPEG). 7 new tests cover parameter plumbing
and default consistency across INPUT_TYPES, save_images(), and
process_image().
