CVE-2025-27154: Spotipy's cache file, containing spotify auth token, is created with overly broad permissions

The CacheHandler class creates a cache file to store the auth token here: https://github.com/spotipy-dev/spotipy/blob/master/spotipy/cache_handler.py#L93-L98

The file created has rw-r--r-- (644) permissions by default, when it could be locked down to rw------- (600) permissions. I think 600 is a sensible default.