COMP: Fix the FFT tests against ITK 6 with wrapping enabled

[hjmjohnson]

Fixes two test failures against ITK 6 built with wrapping enabled. Both tests fail today; neither change is specific to ITK 6 except where guarded.

1. The factory test used a class ITK compiles out

itkVnlComplexToComplex1DFFTImageFilter.h now guards its class with

#if !defined(ITK_LEGACY_REMOVE) && !defined(ITK_FUTURE_LEGACY_REMOVE)

and ITK declares

cmake_dependent_option(ITK_LEGACY_REMOVE "..." OFF "NOT ITK_WRAPPING" ON)

so any ITK built with wrapping forces ITK_LEGACY_REMOVE on and the class
disappears:

error: no template named 'VnlComplexToComplex1DFFTImageFilter' in namespace 'itk'

The class is a deprecated shim that routes to
PocketFFTComplexToComplex1DFFTImageFilter, which is ITK 6's documented default
1D backend. The test now uses the PocketFFT class under
#if ITK_VERSION_MAJOR >= 6, keeping the Vnl spelling for ITK 5.4, which has no
PocketFFT header.

2. The Python test instantiated the 1D filters with one template argument

itk.Forward1DFFTImageFilter[real_image_type]

itk.support.extras.TemplateTypeError: itk.Forward1DFFTImageFilter is not wrapped
for input type `itk.Image[itk.F,3]`.

itkForward1DFFTImageFilter.wrap wraps input and output
(itkForward1DFFTImageFilterIF3ICF3), and itkInverse1DFFTImageFilter.wrap does
the same — identically in ITK 5.4 and ITK 6, so this is not a version change.
The two 1D entries now pass both arguments, matching what the neighbouring
ForwardFFTImageFilter and InverseFFTImageFilter entries in the same list
already do.

Verification

Built against ITK main (6.0.0) with ITK_WRAP_PYTHON=ON, VTK 9.6, macOS
arm64, Metal backend.

	before	after
build	1 failed target	0
ctest	2 of 24 passed	24 of 24

Before these changes the C++ failure stopped the build, so the Python module was
never produced.

🤖 Generated with Claude Code

https://claude.ai/code/session_01S5zzoU6yyUwdLEvjM2s6iS