Add CUSOLVERRF tests to GPU test suite

Include CUSOLVERRF tests in the GPU test suite when the package is available. The tests are conditionally included to avoid failures when CUSOLVERRF.jl is not installed.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: claude

test/gpu/cuda.jl

@@ -106,3 +106,10 @@ end
     prob = LinearProblem(A_gpu_csr, b_gpu)
     sol = solve(prob)
 end
+
+# Include CUSOLVERRF tests if available
+if Base.find_package("CUSOLVERRF") !== nothing
+    @testset "CUSOLVERRF" begin
+        include("cusolverrf.jl")
+    end
+end