Fix set_time_ctrl not doing anything when called twice

[jprochazk]

To repro the original issue on main:

1. call viewer.set_time_ctrl
2. move the time cursor in the viewer somewhere else
3. call viewer_set_time_ctrl again with the same arguments (same time/timeline)

(3) would not adjust the time cursor like in step (1). This is due to _time_ctrl being stateful, but not bidirectionally synchronized between the Viewer and SDK. Moving the time cursor doesn't update the _time_ctrl value back in Python land, and so the _time_ctrl value in (3) isn't changed from (1), resulting in no state update for the Viewer.

For these kinds of things it makes more sense to use custom messages for SDK->Viewer uni-directional things. For Viewer->SDK, we have events exposed for timeline state, which are correctly fired whenever a user input in the Viewer results in the state changing.

[ntjohnson1]

LGTM. I'm going to pull this into my branch and apply the same change for the partition_url update.