Shut down whatever can be shut down

When a worker process stops, it must flush and close the resources it holds: files, caches, database sessions, written by different teams with no common base class. Write two runtime-checkable Protocols, Flushable (flush()) and Closable (close()), and shutdown(resources). For each resource, in order: flush it if it can be flushed, then close it if it can be closed. A failure (OSError) in one step is reported and the shutdown carries on with the next resource. Return one line per resource.