Add a VideoSlice node

[AustinMroz]

Introduces a new "Video Slice" node which allows for restricting a VIDEO input to a provided start_time and duration.

Because remuxing videos requires that start_time is aligned to a keyframe, the existing implementation simply sets reuse_streams to False to utilize the existing architecture. This could be improved in the future to instead stream the transcoding for reduced memory usage.
Similarly, the VideoFromComponents creates a new VideoFromFile with the trimming applied. Since the values for start_time and duration are unlikely to align to an exact frame time, this ensures a subsequent save operation can correctly trim the duration of the last frame and that multiple VideoSlice applied in a row will not accumulate rounding errors.

[Kosinkadink]

Played around with it a bit, is it intended that the node be super picky about there being exactly the duration amount of video sliced? e.g. if a video is 6 seconds long and you try to start to clip a second at 5.5s, it will throw an error that it couldn't be sliced due to not enough footage to slice.

There is definitely use for the error guaranteeing a duration, but the imo the Video interface should also have a boolean input, guarantee_duration default True or something like that, that when set to False would output whatever length clip it could get base on the values.

Also might be nice to support a negative start_time that would start the clip from the end of the video - I can see it being super useful if you want to trim the start without knowing the exact video duration to begin with.

[AustinMroz]

Negative start time is a good idea. I'll add support for it.

I'll update the tooltip for duration to make it clear that 0 disables and investigate your suggestion. Allowing the option for duration less than requested would give closer parity to the VHS equivalent, frame_load_cap.

Worst case, support for less strict duration can be added later without any forward compatibility risk.