fix: implement SII.is_time_dependent for problem types

Author: AayushSabharwal

src/problems/problem_utils.jl

@@ -180,3 +180,6 @@ function Base.summary(io::IO, prob::AbstractPDEProblem)
 end
 
 Base.copy(p::SciMLBase.NullParameters) = p
+
+SymbolicIndexingInterface.is_time_dependent(::AbstractDEProblem) = true
+SymbolicIndexingInterface.is_time_dependent(::AbstractNonlinearProblem) = false