Add support for VIDEO as a built-in type (#7844)

* Add basic support for videos as types

This PR adds support for VIDEO as first-class types. In order to avoid
unnecessary costs, VIDEO outputs must implement the `VideoInput` ABC,
but their implementation details can vary. Included are two
implementations of this type which can be returned by other nodes:

* `VideoFromFile` - Created with either a path on disk (as a string) or
  a `io.BytesIO` containing the contents of a file in a supported format
  (like .mp4). This implementation won't actually load the video unless
  necessary. It will also avoid re-encoding when saving if possible.
* `VideoFromComponents` - Created from an image tensor and an optional
  audio tensor.

Currently, only h264 encoded videos in .mp4 containers are supported for
saving, but the plan is to add additional encodings/containers in the
near future (particularly .webm).

* Add optimization to avoid parsing entire video

* Improve type declarations to reduce warnings

* Make sure bytesIO objects can be read many times

* Fix a potential issue when saving long videos

* Fix incorrect type annotation

* Add a `LoadVideo` node to make testing easier

* Refactor new types out of the base comfy folder

I've created a new `comfy_api` top-level module. The intention is that
anything within this folder would be covered by semver-style versioning
that would allow custom nodes to rely on them not introducing breaking
changes.

* Fix linting issue

folder_paths.py

@@ -4,7 +4,7 @@ import os
 import time
 import mimetypes
 import logging
-from typing import Literal
+from typing import Literal, List
 from collections.abc import Collection
 
 from comfy.cli_args import args
@@ -141,7 +141,7 @@ def get_directory_by_type(type_name: str) -> str | None:
         return get_input_directory()
     return None
 
-def filter_files_content_types(files: list[str], content_types: Literal["image", "video", "audio", "model"]) -> list[str]:
+def filter_files_content_types(files: list[str], content_types: List[Literal["image", "video", "audio", "model"]]) -> list[str]:
     """
     Example:
         files = os.listdir(folder_paths.get_input_directory())