Allow choice of orbit type in SmallManeuverAnalyticalModel
SmallManeuverAnalyticalModel imposes an internal OrbitType
(Keplerian or Equinoctial depending on eccentricity).
This is nice when a user doesn't know which type of orbit he wants to deal with.
However, when one knows which type to use, it's much faster to use this type than to rely on the many conversions the model as to do to go back and forth between types.
As an example, using Keplerian orbits and enforcing the internal type to Keplerian results in a 77% increase in performance for a LEO → GEO low-thrust transfer of 15 days with about 17000 maneuvers (see this forum thread).
So the proposal here is to add constructors to SmallManeuverAnalyticalModel
that will allow the choice of orbit type to use.