fix: construct System in @mtkmodel

Author: AayushSabharwal

src/systems/model_parsing.jl

@@ -7,7 +7,7 @@ ModelingToolkit component or connector with metadata
 $(FIELDS)
 """
 struct Model{F, S}
-    """The constructor that returns ODESystem."""
+    """The constructor that returns a System."""
     f::F
     """
     The dictionary with metadata like keyword arguments (:kwargs), base
@@ -61,7 +61,7 @@ function _model_macro(mod, name, expr, isconnector)
 
     push!(exprs.args, :(variables = []))
     push!(exprs.args, :(parameters = []))
-    push!(exprs.args, :(systems = ODESystem[]))
+    push!(exprs.args, :(systems = System[]))
     push!(exprs.args, :(equations = Union{Equation, Vector{Equation}}[]))
     push!(exprs.args, :(defaults = Dict{Num, Union{Number, Symbol, Function}}()))
 
@@ -114,7 +114,7 @@ function _model_macro(mod, name, expr, isconnector)
     @inline pop_structure_dict!.(
         Ref(dict), [:constants, :defaults, :kwargs, :structural_parameters])
 
-    sys = :($ODESystem($(flatten_equations)(equations), $iv, variables, parameters;
+    sys = :($System($(flatten_equations)(equations), $iv, variables, parameters;
         name, description = $description, systems, gui_metadata = $gui_metadata, defaults))
 
     if length(ext) == 0