Skip preload update for session changes where possible

[Rich-Harris]

As of #554, preload functions take a session object as the second argument, which is the current value of the writable session store whose initial value is provided by the server.

If the store is written to, preload functions are called again and components are updated. This is unnecessary in cases where those functions accept zero or one arguments. (Come to think of it, we can skip rerunning preload altogether if accepts zero arguments, regardless of whether params and query changed — a minor optimisation but worth taking.)