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)
- Read AutoV3 directly from the downloaded file's own file_info hashes
(no SHA256 cross-matching against version_info.files, so the value is
captured even when the API omits SHA256)
- Extract normalize_autov3() validation helper shared with the
sha256-matching autov3_from_civitai_files path
- Fall back to the embedded safetensors header hash at download
completion; mark '' (checked-unavailable) so the startup backfill
query (autov3 IS NULL) never revisits the row
- Clear archive-level AutoV3 for zip-extracted models so per-file
header resolution applies to every extracted model
- Remove calculate_sha256 mocking from download_manager tests since
SHA256 now comes from API metadata (not recalculated during download)
- Update chunk_size assertion from 4MB to 16MB in downloader config test
