PyJWKClient with `cache_keys=True` serves potentially revoked keys

[nick4u]

PyJWKClient initialised with cache_keys=True decorates self.get_signing_key with lru_cache here

functools.lru_cache does not support cached item expiration natively and without it once cached/returned key for given kid will be served "forever".
I believe caching function should have TTL set to lifespan value and also entire cache should be flushed in case jwk_set_cache is updated.