Billboard distanceDisplayCondition with sizeInMeters doesn't work

# BillboardGraphics - DistanceDisplayCondition

Works fine: [Sandcastle - working](https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/#c=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)

Broken: [Sandcastle - broken](https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/#c=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)

When a BillboardGraphics has `distanceDisplayCondition` set it no longer seems to makes the entity disappear, and it seems like the camera is colliding (even clipping the edge in our app) causing the screen to render one colour like the camera is inside something (perhaps inside the billboard?) and eventually the user can get flung back out nearby in the model.

In comparison, in the working example colliding with the billboard just causes the camera to stop moving and the scene/rendering/etc. is all fine.

Start by comparing the working and broken Sandcastle reproductions linked in the issue, focusing on BillboardGraphics with sizeInMeters and distanceDisplayCondition. Trace the relevant billboard visibility and camera-collision behavior from that entry point. Done means the billboard disappears at the configured distance without breaking camera movement or rendering.

Written by the indexing model from the issue text.