tractor/nooz/329.trivial.rst

Add key: Callable[..., Hashable] support to .trionics.maybe_open_context()

Gives users finer grained control over cache hit behaviour using a callable which receives the input kwargs: dict. Further this patch avoids use of the internal Actor._service_n for spawning the entering manager tasks and instead allocates and uses an actor global singleton _Cache.service_n.