a new backend call should be made that hashes many files at once

Currently, for verify, we send to the backend one file at a time, and get back its hash, and compare it to what it should be. This results in a lot of back and forth traffic and processing that has resulted in a significantly slower Verify than in the old launcher.

Therefore, a new backend call should be made that passes a tree of files to the backend to get md5 for, and then returns the checksums of those files to the frontend for comparison. This should result in less back-and-forth overall, and hopefully much better performance. This will require using DirTree to communicate data, since that will result in significantly less text being transmitted in each direction than providing a full file path for every single file.

Start by tracing the existing verify flow that sends one file at a time and compare its frontend and backend boundaries. Review how DirTree is represented, then define the new call around a tree of files and returned checksums. Done means verify can compare the returned MD5 values with less back-and-forth traffic.