Circuit-breaker to suppress Redis connection-refused log flooding on sites where the Redis PHP extension is installed but the server is unreachable (e.g. shared hosting). After the first refused connection, subsequent requests skip retrying silently for 60 seconds, then try again — so at most one error per minute instead of one per page load. Configurable via WP_REDIS_REFUSED_BACKOFF (seconds, default 60; set 0 to disable). Also captures the real PHP error message from the Redis extension instead of the generic 'Connection failed'.