refactor(model): remove some indirection

For small fixed-size structures, it's better to use a slice of values, instead
of a slice of pointers to values: they're stored contiguously and thus can be
iterated on quickly by the CPU, and it does remove an indirection per object
every time the GC kicks in.

internal/storage/api_key.go

@@ -62,7 +62,7 @@ func (s *Storage) APIKeys(userID int64) (model.APIKeys, error) {
 			return nil, fmt.Errorf(`store: unable to fetch API Key row: %v`, err)
 		}
 
-		apiKeys = append(apiKeys, &apiKey)
+		apiKeys = append(apiKeys, apiKey)
 	}
 
 	return apiKeys, nil