add last fm similar artists to db table

+ add db methods for the above
+ try and discard last fm store

app/models/lastfm.py

@@ -0,0 +1,13 @@
+from dataclasses import dataclass
+
+
+@dataclass
+class SimilarArtist:
+    artisthash: str
+    similar_artist_hashes: str
+
+    def get_artist_hash_set(self) -> set[str]:
+        """
+        Returns a set of similar artists.
+        """
+        return set(self.similar_artist_hashes.split("~"))