making ocPreds more efficient

[audreyyeoCH]

Make these more efficient:

                               user    system      elapsed

ocPredprobDist 165.489 0.012 165.510
plotOc 57.410 0.002 57.414
ocRctPredprobDist 22.048 0.006 22.055

it's probably only ocPredprobDist as the others build on it

May 2025 results :

Examples with CPU (user + system) or elapsed time > 5s
user system elapsed
ocPredprobDist 165.726 0.011 165.774
plotOc 58.122 0.005 58.134
ocRctPredprobDist 22.139 0.003 22.144

[danielinteractive]

Also #134 does not really close this issue, because we don't really make the simulations more efficient there, we just run less of them. So I would still keep this issue open.