Try and improve responsiveness when debounced isn't really needed

[astrofrog]

The main motivation for @debounced is to avoid many repeated updates when e.g. panning/zooming or doing other front-end changes. However, currently, there are cases where relying on debounced is not desirable, e.g.:

image.state.reset_limits()
time.sleep(3)

In this case, if this code is in a cell, the figure won't be updated until after the sleep because the callback for the debounced update is not in a separate thread. The long-term fix would be to try and make sure glue and glue-jupyter are thread-safe and use a thread in this case, but for now, a simple fix is to simply treat updates in limits similarly to e.g. updates in percentile, cmap and so on, and make sure those changes result in an immediate update in the figure.

This PR also adds a check to avoid unnecessary repeated updates in .update()

[bmorris3]

Thanks @astrofrog, this is helpful 🙌🏻