flipbook bug for CEGS

When more than one flipbooked ceg fires off at the same time, the flipbook has a split second where it shows the whole thing on all the explosions from what I can tell.

It is perfectly fine when it's just one tank firing it, but when more than one tank starts shooting, the impact just gets bugged out.

https://github.com/user-attachments/assets/32d76037-a569-4cfb-8b7a-8c17dbde7eae

Start by reproducing the attached flipbook effect with multiple tanks firing simultaneously, comparing it with a single-tank firing case. Trace the CEGS flipbook rendering path and use the reported behavior as the success criterion: simultaneous impacts should not briefly display the whole flipbook.

Written by the indexing model from the issue text.