Alternator efficiency for HEVs (applies fc aux load only)

[kylecarow]

This PR fixes a small bug I found where HEVs/PHEVs did not account for alternator efficiency in aux power loads coming supplied by the fuel converter. Aux loads supplied by the RES are assumed to be all electric as is our assumption for BEVs so there is no alternator to account for there.

In fact, we did not even have an alternator efficiency in the HybridElectricVehicle at all, so this PR adds that and makes a default of 100% to maintain compatibility with existing vehicle files (that would otherwise have a missing field and fail to deserialize). There is also a test to make sure this works as expected. Maybe we can add a logging event letting the user know the default value of 100% was used? I anticipate getting rid of this serde default as soon as we switch to a break in the vehicle file format (next major version?)

A hiccup I predict with this change: if we want to model fuel cells in FASTSim 3 as HEVs (but have a different powertrain type, just like we do for PHEVs), then having an alternator efficiency in the HybridElectricVehicle doesn't exactly make sense, as they have no alternator. We can enforce this field to be 100% but I really don't like the idea of having fields that don't apply - that feels like a FASTSim-2-ism.

• We could just make the alt_eff for HEVs Option<si::Ratio> instead, and make None unwrap to 100%
• Relevant Tracking issue for fuel cell electric vehicles #270

I also dont like how we model alternator as a ratio rather than an interpolator. Could we support alternators that have varying efficiency based on power load? FC temperature as a surrogate?

[kylecarow]

Should probably rebase these changes on #279 and implement this as a vehicle-wide aux load efficiency penalty

[kylecarow]

#286 is a better approach