Fix plan leak in cuTENSOR tensortrace!

ext/TensorOperationscuTENSORExt.jl

@@ -220,7 +220,9 @@ function TO.tensortrace!(
 
     # map to reduction operation
     plan = plan_trace(A, Ainds, opA, C, Cinds, OP_IDENTITY, OP_ADD)
-    return reduce!(plan, α, A, β, C)
+    reduce!(plan, α, A, β, C)
+    CUDACore.unsafe_free!(plan) # the plan-taking `reduce!` does not free the plan
+    return C
 end
 
 function cuTENSOR.CuTensorDescriptor(

test/cutensor.jl

@@ -576,6 +576,28 @@ if cuTENSOR.functional()
         end
     end
 
+    @testset "tensortrace! does not leak plans" begin
+        # each leaked plan holds on to a 128 KiB reduction workspace
+        A = CuArray(randn(Float32, 64, 64, 64, 64))
+        C = CUDACore.zeros(Float32, 64, 64)
+        @tensor C[a, b] = A[a, c, b, c] # warm up
+
+        GC.gc(true)
+        CUDACore.reclaim()
+        CUDACore.synchronize()
+        GC.enable(false)
+        try
+            live0 = CUDACore.memory_stats().live
+            for _ in 1:1000
+                @tensor C[a, b] = A[a, c, b, c]
+            end
+            CUDACore.synchronize()
+            @test CUDACore.memory_stats().live - live0 < 2^20 # would be 125 MiB if leaking
+        finally
+            GC.enable(true)
+        end
+    end
+
     @testset "Issues" verbose = true begin
         @testset "Issue PR #186" begin
             # https://github.com/Jutho/TensorOperations.jl/pull/186