Avoid re-running premission for off-design

[jkirk5]

Desired capability or behavior.

From @cmbenne3 in #772
The off design mission analysis currently instantiates a whole new aviary problem object and re-runs the entirety of the pre-mission block. This is not really necessary (particularly for subsystem masses) which are not expected to change from the initial design mission. Since all these parameters are recalculated the aircraft is basically being re-designed (although if everything is correct it re-designs to be identical to the sizing aircraft). We might want to refactor the code to avoid these extra calculations.

We should also consider the multi-mission architecture and look for ways to align off design with it since there is some similarity in output.

Is your feature request related to a problem? Please describe.

No response

Associated Bug Report

No response

[jkirk5]

The "correct" way to do this is probably come up with an overall way to specify which core parts of an AviaryProblem (Pre-mission, mission, post-mission) should run, then use that existing feature in off-design. That's a major refactor but would be very beneficial for future Aviary