Improve MSFR Griffin+Pronghorn simulation speed

[GiudGiud]

Right now the precursor advection is lumped in with the NS simulation. This slows down the fluid solve by 3x, unnecessarily. We can already use a MultiApp to separate the precursor solve and advect them using auxiliary variables.

However, the ideal set up would leverage sibling transfer for the coupling, to have Griffin be the main app and use up-to-date information for precursor advection (latest fission source, latest velocities).

This is a WIP in MOOSE, we will wait till this is ready to update those inputs, and have much more tenable runtimes.