PRP - Patchouli Book Loading Fix

After Patchouli changed to store books in the /data/ folder, external resource packs or data packs lost the ability to override the contents of these books.

This mod uses mixin technology to change Patchouli's loading behavior, making it first attempt to load books from the assets folder, and only then from data.

Especially relevant for Patchouli version 1.18.x: some mods (such as Apothesis) still place their manuals in the legacy data folder, and in this situation Patchouli doesn't even try to load files from resource packs, so this fix is necessary.

Useful only for non-English speaking players or those who want to apply resource packs to Patchouli books.