v9.39.0

ModelingToolkit v9.39.0

Diff since v9.38.0

Merged pull requests:

• Move labelledarrays to extension testing (#3031) (@ChrisRackauckas)
• Run initialization on ODEs with superset initial conditions (#3032) (@AayushSabharwal)
• Add unit aware diff2term (#3034) (@YingboMa)
• Throw an error if structural simplification is applied twice (take 2) (#3035) (@YingboMa)

Closed issues:

• Inconsistency for how to give intiial conditions to DAEs with higher order derivatives. (#2619)
• Variables introduced during simplification of 2nd order to first order dont have the correct units. (#2959)
• Array variable units (#3009)