Add disk inverse unit test

Author: Copilot

test/libfasttransformstests.jl

@@ -171,6 +171,9 @@ FastTransforms.ft_set_num_threads(ceil(Int, Base.Sys.CPU_THREADS/2))
     ps = plan_disk_synthesis(A)
     pa = plan_disk_analysis(A)
     test_nd_plans(p, ps, pa, A)
+    @test inv(pa) isa typeof(ps)
+    @test inv(pa)*(p*A) ≈ ps*(p*A)
+    @test p\(pa*(inv(pa)*(p*A))) ≈ A
     A = diskones(Float64, n, 4n-3) + im*diskones(Float64, n, 4n-3)
     p = plan_disk2cxf(A, α, β)
     ps = plan_disk_synthesis(A)