Added context window support to core sampling code (Comfy-Org#9238)

* Added initial support for basic context windows - in progress

* Add prepare_sampling wrapper for context window to more accurately estimate latent memory requirements, fixed merging wrappers/callbacks dicts in prepare_model_patcher

* Made context windows compatible with different dimensions; works for WAN, but results are bad

* Fix comfy.patcher_extension.merge_nested_dicts calls in prepare_model_patcher in sampler_helpers.py

* Considering adding some callbacks to context window code to allow extensions of behavior without the need to rewrite code

* Made dim slicing cleaner

* Add Wan Context WIndows node for testing

* Made context schedule and fuse method functions be stored on the handler instead of needing to be registered in core code to be found

* Moved some code around between node_context_windows.py and context_windows.py

* Change manual context window nodes names/ids

* Added callbacks to IndexListContexHandler

* Adjusted default values for context_length and context_overlap, made schema.inputs definition for WAN Context Windows less annoying

* Make get_resized_cond more robust for various dim sizes

* Fix typo

* Another small fix

Author: Kosinkadink