GitLab

* Enhance type hints and docstrings in scheduling_ddpm.py

- Added type hints for function parameters and return types across the DDPMScheduler class and related functions.
- Improved docstrings for clarity, including detailed descriptions of parameters and return values.
- Updated the alpha_transform_type and beta_schedule parameters to use Literal types for better type safety.
- Refined the _get_variance and previous_timestep methods with comprehensive documentation.

* Refactor docstrings and type hints in scheduling_ddpm.py

- Cleaned up whitespace in the rescale_zero_terminal_snr function.
- Enhanced the variance_type parameter in the DDPMScheduler class with improved formatting for better readability.
- Updated the docstring for the compute_variance method to maintain consistency and clarity in parameter descriptions and return values.

* Apply `make fix-copies`

* Refactor type hints across multiple scheduler files

- Updated type hints to include `Literal` for improved type safety in various scheduling files.
- Ensured consistency in type hinting for parameters and return types across the affected modules.
- This change enhances code clarity and maintainability.