Fix two CI failures in unified RosenbrockCache

1. strip_cache override: the generic implementation calls
   constructorof(cache)(nothing × 29) which fails for RosenbrockCache
   because dense/ks/dtC/dtd require Vector/Matrix types and
   interp_order requires Int. Add an explicit override that
   constructs a Nothing-typed cache.

2. Val{1} interpolants: all four _ode_interpolant derivative
   functions were missing the interp_order == -1 branch. When
   Rosenbrock23/32 (which have empty H → interp_order = -1) hit
   the else branch it accessed k[3] but only 2 k-vectors exist,
   causing a BoundsError. Add the Hermite derivative formula as
   the first branch in each function.

Author: Harsh Singh

lib/OrdinaryDiffEqRosenbrock/src/rosenbrock_caches.jl

@@ -247,6 +247,30 @@ function get_fsalfirstlast(
     return (cache.fsalfirst, cache.fsallast)
 end
 
+function OrdinaryDiffEqCore.strip_cache(cache::RosenbrockCache)
+    return RosenbrockCache{
+        Nothing, Nothing, Nothing, Nothing, Nothing, Nothing,
+        Nothing, Nothing, Nothing, Nothing, Nothing, Nothing,
+        Nothing, Nothing, Nothing, Nothing,
+    }(
+        nothing, nothing,
+        Vector{Nothing}(undef, 0),
+        nothing, nothing, nothing,
+        Matrix{Nothing}(undef, 0, 0),
+        Vector{Nothing}(undef, 0),
+        Vector{Nothing}(undef, 0),
+        nothing, nothing, nothing,
+        nothing, nothing,
+        nothing, nothing, nothing,
+        nothing, nothing, nothing,
+        nothing, nothing,
+        nothing, nothing,
+        nothing, nothing,
+        nothing, nothing,
+        0,
+    )
+end
+
 ################################################################################
 
 ### Tsit5DA - hybrid explicit/linear-implicit method for DAEs

lib/OrdinaryDiffEqRosenbrock/src/rosenbrock_interpolants.jl

@@ -145,7 +145,14 @@ end
         },
         idxs::Nothing, T::Type{Val{1}}, differential_vars
     )
-    if !hasproperty(cache, :interp_order) || cache.interp_order == 2
+    if hasproperty(cache, :interp_order) && cache.interp_order == -1
+        # Hermite derivative: d/dt of Θ1*y₀ + Θ*y₁ + Θ*(Θ-1)*[(1-2Θ)*(y₁-y₀) + (Θ-1)*dt*k[1] + Θ*dt*k[2]]
+        @.. (
+            (-y₀ + y₁) +
+                (2Θ - 1) * ((1 - 2Θ) * (y₁ - y₀) + (Θ - 1) * dt * k[1] + Θ * dt * k[2]) +
+                Θ * (Θ - 1) * (-2 * (y₁ - y₀) + dt * (k[1] + k[2]))
+        ) / dt
+    elseif !hasproperty(cache, :interp_order) || cache.interp_order == 2
         @.. (k[1] + Θ * (-2 * k[1] + 2 * k[2] - 3 * k[2] * Θ) - y₀ + y₁) / dt
     elseif cache.interp_order == 4
         @.. (
@@ -177,7 +184,16 @@ end
         },
         idxs, T::Type{Val{1}}, differential_vars
     )
-    if !hasproperty(cache, :interp_order) || cache.interp_order == 2
+    if hasproperty(cache, :interp_order) && cache.interp_order == -1
+        @views @.. (
+            (-y₀[idxs] + y₁[idxs]) +
+                (2Θ - 1) * (
+                (1 - 2Θ) * (y₁[idxs] - y₀[idxs]) + (Θ - 1) * dt * k[1][idxs] +
+                    Θ * dt * k[2][idxs]
+            ) +
+                Θ * (Θ - 1) * (-2 * (y₁[idxs] - y₀[idxs]) + dt * (k[1][idxs] + k[2][idxs]))
+        ) / dt
+    elseif !hasproperty(cache, :interp_order) || cache.interp_order == 2
         @views @.. (
             k[1][idxs] +
                 Θ * (-2 * k[1][idxs] + 2 * k[2][idxs] - 3 * k[2][idxs] * Θ) -
@@ -215,7 +231,13 @@ end
         },
         idxs::Nothing, T::Type{Val{1}}, differential_vars
     )
-    if !hasproperty(cache, :interp_order) || cache.interp_order == 2
+    if hasproperty(cache, :interp_order) && cache.interp_order == -1
+        @.. out = (
+            (-y₀ + y₁) +
+                (2Θ - 1) * ((1 - 2Θ) * (y₁ - y₀) + (Θ - 1) * dt * k[1] + Θ * dt * k[2]) +
+                Θ * (Θ - 1) * (-2 * (y₁ - y₀) + dt * (k[1] + k[2]))
+        ) / dt
+    elseif !hasproperty(cache, :interp_order) || cache.interp_order == 2
         @.. out = (k[1] + Θ * (-2 * k[1] + 2 * k[2] - 3 * k[2] * Θ) - y₀ + y₁) / dt
     elseif cache.interp_order == 4
         @.. out = (
@@ -249,7 +271,16 @@ end
         },
         idxs, T::Type{Val{1}}, differential_vars
     )
-    if !hasproperty(cache, :interp_order) || cache.interp_order == 2
+    if hasproperty(cache, :interp_order) && cache.interp_order == -1
+        @views @.. out = (
+            (-y₀[idxs] + y₁[idxs]) +
+                (2Θ - 1) * (
+                (1 - 2Θ) * (y₁[idxs] - y₀[idxs]) + (Θ - 1) * dt * k[1][idxs] +
+                    Θ * dt * k[2][idxs]
+            ) +
+                Θ * (Θ - 1) * (-2 * (y₁[idxs] - y₀[idxs]) + dt * (k[1][idxs] + k[2][idxs]))
+        ) / dt
+    elseif !hasproperty(cache, :interp_order) || cache.interp_order == 2
         @views @.. out = (
             k[1][idxs] +
                 Θ *