implement loos coupling to 3rd party module

[safhac]

the current CompositionRenderer is tightly coupled to moviepy, the render method returns a moviepy CompositeVideoClip

class CompositionRenderer:
   ...
   async def render((self, composition: CompositionSpec) -> CompositeVideoClip:

fix the design flaw by implementing a loosely coupled dependency to allow other frameworks e.g ffmpeg-python