Allow multiple `xfoilAnalysis` instances

Purpose

Previously, all instances of xfoilAnalysis would use the same XFOIL global variables. This caused conflicts if the two instances had different flight conditions, airfoil shapes, etc. This update changes pyXLIGHT to use the same method as ADflow to make a separate copy of XFOIL for every xfoilAnalysis class instance.

Type of change

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Bugfix (non-breaking change which fixes an issue)

Testing

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Checklist

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[x] I have run unit and regression tests which pass locally with my changes
[ ] I have added new tests that prove my fix is effective or that my feature works
[ ] I have added necessary documentation

mdolab / CMPLXFOIL