GitLab

* Enhance type hints and docstrings in LMSDiscreteScheduler class

Updated type hints for function parameters and return types to improve code clarity and maintainability. Enhanced docstrings for several methods, providing clearer descriptions of their functionality and expected arguments. Notable changes include specifying Literal types for certain parameters and ensuring consistent return type annotations across the class.

* docs: Add specific paper reference to `_convert_to_karras` docstring.

* Refactor `_convert_to_karras` docstring in DPMSolverSDEScheduler to include detailed descriptions and a specific paper reference, enhancing clarity and documentation consistency.