Consider other image comparison algorithm

I see that there is a script called "butteraugli" that compare two images and give a score : https://github.com/google/butteraugli

I think that could be an interesting addition for jpeg-recompress.

Review jpeg-recompress and the linked Google butteraugli project to understand the current image-comparison path and the proposed alternative. No files or tests are named, so first identify the relevant entry points and define integration and acceptance criteria; done would mean butteraugli is meaningfully supported without disrupting existing JPEG archival behavior.

Written by the indexing model from the issue text.