Delayed neutrons are emitted promptly

[gridley]

Bug Description

I have not written any test cases, but we can see that in physics.cpp's sample_fission_neutron, in the delayed case, the decay time is not sampled and added on to the site's time entry.

To resolve

Sample a decay time for the precursor, and add that value to site.time. This alters the random number stream, so some means of preserving the prior RNG stream would be needed, too.

[ilhamv]

This one is addressed in #2898.

As for the changing random number stream, the plan is to group the PR along with other PRs that also change the stream, like #2992, and then revise the regression test keys (as discussed in #2898).

[gridley]

Closing b/c this is a duplicate. Doh! I will review your code after I submit my PhD thesis around August 13, Ilham! Sorry your stuff has stayed open for so long. It's not a lot of code, but I need to take a little more time to understand exactly what it's doing fully.