Can't set time range on individual entities via blueprint api

[Wumpf]

Adding this to the helix demo doesn't have any effect right now:

    blueprint = rrb.Blueprint(
        rrb.Spatial3DView(
            origin="/",
            overrides={
                "helix/structure/scaffolding/beads": [
                    rrb.VisibleTimeRange(
                        "stable_time",
                        start=rrb.TimeRangeBoundary.cursor_relative(seconds=-0.3),
                        end=rrb.TimeRangeBoundary.cursor_relative(seconds=0.3),
                    ),
                ]
            },
        ),
    )
    rr.send_blueprint(blueprint)

We store it already in the blueprint but it's stored on "recursive override path" which is a vestigue from back when we tried a model of "indidual & recursive" overrides. We dumped that idea and instead want to make overrides be path-expression enabled in the future. Individua/recursive is really only used for recursive visibility & interactivity today and we should clean up everything else. See:

• Support full entity-path-expressions for overrides #6673

Python blueprint api overrides use only the "individual" override path.

-> The fix MIGHT be as easy to change these two code paths to use "individual" instead. But a bit more looking into is needed

• rerun/crates/viewer/re_viewport_blueprint/src/view_contents.rs

  Line 541 in 19e93a6

  &recursive_override_path,

• rerun/crates/viewer/re_selection_panel/src/visible_time_range_ui.rs

  Line 47 in 19e93a6

  let override_path = data_result.recursive_override_path();

We also should really add a test for this - at least a release_checklist one