Instead of doing 16 pseudo-raycasts per second, lower it to a max
of 4, and don't do "catch up" raycasts if we are stepping at a
slower rate than that, just increase the weight of the current
cast to account for the entire time frame.
This will reduce the precision of radiation detection in the short
run, but is probably still good enough, especially with radiation
simulation already being very probabilistic.
This will hopefully mitigate per-player performance load on more
heavily loaded servers with many players.
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