Add @lru_cache to some functions

The stats after importing 30k releases are:
convert_area: CacheInfo(hits=29962, misses=77, maxsize=100, currsize=77)
convert_artist_credit: CacheInfo(hits=22775, misses=7225, maxsize=5000, currsize=5000)
Convert recordings as well
Only look at extrapaths if wscompat is on