v8.39.0

ModelingToolkit v8.39.0

Diff since v8.38.0

Closed issues:

• Tests for Index Reduction and SCC fail (#2012)

Merged pull requests:

• Prevent repeated call of substituter(rules) in substitute. (#1963) (@evetion)
• consistent namespacing in add_input_disturbance (#1986) (@baggepinnen)
• pass analytic to ODEFunction (#1996) (@xtalax)
• Add copy method for SystemStructure (#1999) (@Keno)
• Allow empty inputs in generate_control_function (#2004) (@baggepinnen)
• add an example for parsing Julia expressions into ModelingToolkit solves (#2008) (@ChrisRackauckas)
• dummy_derivatives: Reset eqcolor every loop (#2011) (@Keno)
• [docs] Change plot vars to idxs (#2014) (@xlxs4)
• Add unknown_states (#2016) (@YingboMa)