Loadout selection no longer has two (disagreeing) implementations. What
the UI shows is now what the miz will have.
We now store the chosen layout in the Flight *always*, not just for
custom loadouts. This means that we do loadout lookups at the start of
each turn, but the data is cached in pydcs.
Era-specific loadout degradation is still done at generation (and
presentation) time. This is so that players can toggle that option and
have it affect the *current* turn, rather than the next one.
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