This fixes a few issues:

• There were some typescript warnings related to atproto types which are fixed.
• There was an error using the image-size module to get aspect ratios when migrating images. I've removed that dependency (yay one less dependency) and replaced it with a simple function that looks like dimensions for PNGs and JPGs.
• There was an error migrating videos. I'm not sure when this changed, but for some reason, mp4 video mime types were being reported as "application/mp4" but atproto requires the mime type to be "video/mp4". So I just made it use "video/mp4" if the mime type was "application/mp4", and that fixes it.
• When migrating a tweet with multiple animated gifs in it, this now only migrates the first animated gif. It's because 1) animated gifs in X are technically mp4 videos, not gifs, and 2) atproto only supports one video per post.

Test plan

• In a test X account, make several posts that includes photos, videos, and animated gifs, including one post with multiple animated gifs.
• Try migrating them to Bluesky. It should all work without errors.