feat: lexicographically sort equations in structural_simplify

Author: AayushSabharwal

src/systems/systemstructure.jl

@@ -352,6 +352,10 @@ function TearingState(sys; quick_cancel = false, check = true)
         end
     end
 
+    # sort equations lexicographically to reduce simplification issues
+    # depending on order due to NP-completeness of tearing.
+    sort!(eqs, by = string)
+
     ### Handle discrete variables
     lowest_shift = Dict()
     for var in fullvars