Add set_image for updating the image content of an existing frame

[daveisfera]

When updating the content of a video, this is more efficient because the existing frame can be used

[daveisfera]

This isn't useful like I had hoped and will require some additional work to be valuable.
The current to_image and from_image functions have an implied use of RGB format, so it's not a drop in replacement to use the existing frame, because calling set_image on it is trying to copy into a YUV image in the tests I've done and the current copy_bytes_to_plane appears to be assuming RGB so it doesn't work.