raise peer max metasize (torrent file) size to 100mib

Perhaps the 4MiB metadata limit made sense when it was introduced years ago, but with modern storage devices easily being over 10TB more and more 1TB+ torrents can be found in the wild. These torrent files (metadata) are easily over 4MiB.

This patch raises the limit to 100MiB. Raising the limit in the end only delays the problem for a few decades or so, as storage density only keeps increasing and files keep growing in size. A more permanent solution without arbitrary limits would be ideal.

Fixes https://bugs.kde.org/show_bug.cgi?id=392202, where the reporter mentions Touhou Lossless Music Collection, which is a ~9MiB torrent for version 19 of the main part of the collection.

Check initially introduced in c743f5e1.