provide default handler for async_update_records_complete in _ServiceBrowserBase

async_update_records_complete is no longer an abstract method in _ServiceBrowserBase and a default handler is now provided which was originally in AsyncServiceBrowser. This allows us to cythonize the function and use the fast PyDict methods since its called so frequently when a browser is running.

It is still expected that async_update_records_complete can be overridden in subclasses, but it is recommended to subclass ServiceBrowser or AsyncServiceBrowser directly instead of _ServiceBrowserBase since the _ indicates _ServiceBrowserBase is protected and its internal api is not public (or stable)