Fix retcode comparison to use SciMLBase.successful_retcode

The retcode comparison `sol.retcode != :Success` was comparing a
`SciMLBase.ReturnCode.T` enum value against a Symbol, which always
evaluates to `true` (they are different types). This caused the
`DataDrivenProblem(::DESolution)` constructor to always throw an
AssertionError, even for successful solves.

Replace with `DiffEqBase.SciMLBase.successful_retcode(sol)` which is
the modern SciML API for checking solution success.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: claude

src/problem/type.jl

@@ -518,7 +518,7 @@ function DataDrivenProblem(
         sol::T; use_interpolation = false,
         kwargs...
     ) where {T <: DiffEqBase.DESolution}
-    if sol.retcode != :Success
+    if !DiffEqBase.SciMLBase.successful_retcode(sol)
         throw(AssertionError("The solution is not successful. Abort."))
         return
     end