final tidying before marking PR as ready for review

- Replace AnyModelLoader with ModelLoaderRegistry
- Fix type check errors in multiple files
- Remove apparently unneeded `get_model_config_enum()` method from model manager
- Remove last vestiges of old model manager
- Updated tests and documentation

resolve conflict with seamless.py

invokeai/backend/model_manager/merge.py

@@ -13,7 +13,7 @@ from typing import Any, List, Optional, Set
 
 import torch
 from diffusers import AutoPipelineForText2Image
-from diffusers import logging as dlogging
+from diffusers.utils import logging as dlogging
 
 from invokeai.app.services.model_install import ModelInstallServiceBase
 from invokeai.backend.util.devices import choose_torch_device, torch_dtype
@@ -76,7 +76,7 @@ class ModelMerger(object):
                 custom_pipeline="checkpoint_merger",
                 torch_dtype=dtype,
                 variant=variant,
-            )
+            )  # type: ignore
             merged_pipe = pipe.merge(
                 pretrained_model_name_or_path_list=model_paths,
                 alpha=alpha,