Follow XDG directory specifications

[toastal]

https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

${SORRI_CACHE_DIR_PREFIX:-$HOME/.cache/sorri/${SORRI_CACHE_NAME}}" does not follow the spec for users may want their caches. Use $XDG_CACHE_DIR as the highest priority and fallback to $HOME after.