Planetary EoS selection improvements

Currently, the user has to choose in the .yml which type(s) of EoS to load. It's clunky and means loading e.g. all ANEOS material tables even if only one material is needed. Could solve by selecting instead which specific materials are needed, or even perhaps checking the initial conditions material IDs directly.

If not the latter, then should also include a check that the correct EoS have been perpared for the particles. e.g. can get seg faults if a tabular EoS isn't loaded.

A small aside: the EoS is also currently needed when running the stand-alone FoF for writing the snapshot, which may seem odd to a user (used when writing the snapshot), but should also be fixed by the above anyway.