refactor: make dependent and numeric portions singletons

Author: AayushSabharwal

src/systems/index_cache.jl

@@ -8,8 +8,10 @@ function BufferTemplate(s::Type{<:Symbolics.Struct}, length::Int)
     BufferTemplate(T, length)
 end
 
-const DEPENDENT_PORTION = :dependent
-const NONNUMERIC_PORTION = :nonnumeric
+struct Dependent <: SciMLStructures.AbstractPortion end
+struct Nonnumeric <: SciMLStructures.AbstractPortion end
+const DEPENDENT_PORTION = Dependent()
+const NONNUMERIC_PORTION = Nonnumeric()
 
 struct ParameterIndex{P, I}
     portion::P

src/systems/parameter_buffer.jl

@@ -210,7 +210,8 @@ SciMLStructures.ismutablescimlstructure(::MTKParameters) = true
 
 for (Portion, field) in [(SciMLStructures.Tunable, :tunable)
                          (SciMLStructures.Discrete, :discrete)
-                         (SciMLStructures.Constants, :constant)]
+                         (SciMLStructures.Constants, :constant)
+                         (Nonnumeric, :nonnumeric)]
     @eval function SciMLStructures.canonicalize(::$Portion, p::MTKParameters)
         as_vector = buffer_to_arraypartition(p.$field)
         repack = let as_vector = as_vector, p = p