fix: improve type-stability of ImperativeAffect

Author: AayushSabharwal

src/systems/imperative_affect.jl

@@ -85,10 +85,16 @@ context(a::ImperativeAffect) = a.ctx
 observed(a::ImperativeAffect) = a.obs
 observed_syms(a::ImperativeAffect) = a.obs_syms
 function discretes(a::ImperativeAffect)
-    Iterators.filter(ModelingToolkit.isparameter,
-        Iterators.flatten(Iterators.map(
-            x -> symbolic_type(x) == NotSymbolic() && x isa AbstractArray ? x : [x],
-            a.modified)))
+    discs = SymbolicT[]
+    for val in a.modified
+        val = unwrap(val)
+        if val isa SymbolicT
+            isparameter(a) && push!(discs, val)
+        elseif val isa AbstractArray
+            append!(discs, filter(isparameter, map(unwrap, val)))
+        end
+    end
+    return discs
 end
 modified(a::ImperativeAffect) = a.modified
 modified_syms(a::ImperativeAffect) = a.mod_syms