fix: improve type-stability of some SII functions

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -170,17 +170,20 @@ function SymbolicIndexingInterface.variable_symbols(sys::AbstractSystem)
     return unknowns(sys)
 end
 
-function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym)
-    sym = unwrap(sym)
+function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym::Union{Num, Symbolics.Arr, Symbolics.CallAndWrap})
+    is_parameter(sys, unwrap(sym))
+end
+
+function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym::Int)
+    sym in 1:length(parameter_symbols(sys))
+end
+
+function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym::SymbolicT)
     if has_index_cache(sys) && (ic = get_index_cache(sys)) !== nothing
         return sym isa ParameterIndex || is_parameter(ic, sym) ||
-               iscall(sym) &&
-               operation(sym) === getindex &&
+               iscall(sym) && operation(sym) === getindex &&
                is_parameter(ic, first(arguments(sym)))
     end
-    if unwrap(sym) isa Int
-        return unwrap(sym) in 1:length(parameter_symbols(sys))
-    end
     return any(isequal(sym), parameter_symbols(sys)) ||
            hasname(sym) && !(iscall(sym) && operation(sym) == getindex) &&
            is_parameter(sys, getname(sym))
@@ -191,7 +194,7 @@ function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym::Symbol
         return is_parameter(ic, sym)
     end
 
-    named_parameters = [getname(x)
+    named_parameters = Symbol[getname(x)
                         for x in parameter_symbols(sys)
                         if hasname(x) && !(iscall(x) && operation(x) == getindex)]
     return any(isequal(sym), named_parameters) ||