ENH: Ingest ITKHigherOrderAccurateGradient into Modules/Filtering

[hjmjohnson]

Ingest the standalone remote module
InsightSoftwareConsortium/ITKHigherOrderAccurateGradient
into Modules/Filtering/HigherOrderAccurateGradient/. Header-only filter
that computes higher-order accurate centered finite differences of
arbitrary even order on N-dimensional scalar images. In-tree under
EXCLUDE_FROM_DEFAULT.

Built directly on upstream/main via the v4 ingestion pipeline (#6204).

Commits

#	Subject
1	ENH: Ingest ITKHigherOrderAccurateGradient into Modules/Filtering (Mode-A merge)
2	DOC: Add HigherOrderAccurateGradient README pointing at upstream
3	COMP: Remove HigherOrderAccurateGradient .remote.cmake (in-tree)
4	ENH: Enable Module_HigherOrderAccurateGradient in configure-ci

Merge topology preserved: 3 merge commits, 42 commits unique to this PR.

Phase B follow-up

After merge, archive the upstream repo via the v4 archive script:

Utilities/Maintenance/RemoteModuleIngest/archive-remote-module.sh \
    HigherOrderAccurateGradient

[hjmjohnson]

@greptile please review

[greptile-apps]

Greptile Summary

Ingests the ITKHigherOrderAccurateGradient remote module into Modules/Filtering/HigherOrderAccurateGradient/ as a first-class in-tree module and removes the corresponding .remote.cmake entry. The module is registered as EXCLUDE_FROM_DEFAULT and enabled explicitly in the CI configure step.

• New headers: HigherOrderAccurateDerivativeOperator, HigherOrderAccurateDerivativeImageFilter, and HigherOrderAccurateGradientImageFilter — all header-only, implementing centered finite-difference kernels of arbitrary even order on N-D scalar images.
• Removed: Modules/Remote/HigherOrderAccurateGradient.remote.cmake; pyproject.toml gains the corresponding -DModule_HigherOrderAccurateGradient:BOOL=ON flag.

Confidence Score: 4/5

Safe to merge after addressing the zero-accuracy guard; all other code is a faithful in-tree ingestion of a working remote module.

The coefficient generator writes past the end of the coefficient vector when m_OrderOfAccuracy is 0 — unsigned underflow on order-1 produces a near-UINT_MAX index, causing a definite crash. The default value of 2 protects typical users, but the API accepts 0 with no diagnostic.

itkHigherOrderAccurateDerivativeOperator.hxx — GenerateFirstOrderCoefficients needs an order==0 guard.

Important Files Changed

Filename	Overview
Modules/Filtering/HigherOrderAccurateGradient/include/itkHigherOrderAccurateDerivativeOperator.hxx	GenerateFirstOrderCoefficients() has an out-of-bounds access when m_OrderOfAccuracy==0: coeff[order+1] and coeff[order-1] are written to index 1 and UINT_MAX respectively on a length-1 vector.
Modules/Filtering/HigherOrderAccurateGradient/itk-module.cmake	ITKImageGradient and ITKImageIntensity are listed in DEPENDS but only needed by the test executables; ITKSmoothing (for NeighborhoodOperatorImageFilter) is absent from DEPENDS.
Modules/Filtering/HigherOrderAccurateGradient/include/itkHigherOrderAccurateDerivativeImageFilter.hxx	Mini-pipeline implementation looks correct; spacing guard, progress accumulator, and region-padding are all present.
Modules/Filtering/HigherOrderAccurateGradient/include/itkHigherOrderAccurateGradientImageFilter.hxx	DynamicThreadedGenerateData follows the same slice-based operator pattern as ITK's stock GradientImageFilter; direction handling looks correct.
Modules/Remote/HigherOrderAccurateGradient.remote.cmake	Remote cmake entry correctly deleted now that the module is ingested in-tree.
pyproject.toml	Correctly enables Module_HigherOrderAccurateGradient in the CI configure line.

Class Diagram

%%{init: {'theme': 'neutral'}}%%
classDiagram
    class NeighborhoodOperator {
        <<abstract>>
        +CreateDirectional()
        +FlipAxes()
        +ScaleCoefficients()
    }
    class HigherOrderAccurateDerivativeOperator {
        -m_Order : unsigned int
        -m_OrderOfAccuracy : unsigned int
        +SetOrder()
        +SetOrderOfAccuracy()
        #GenerateCoefficients() CoefficientVector
        -GenerateFirstOrderCoefficients() CoefficientVector
    }
    class ImageToImageFilter {
        <<abstract>>
    }
    class HigherOrderAccurateDerivativeImageFilter {
        -m_Order : unsigned int
        -m_OrderOfAccuracy : unsigned int
        -m_Direction : unsigned int
        -m_UseImageSpacing : bool
        +GenerateData()
        +GenerateInputRequestedRegion()
    }
    class HigherOrderAccurateGradientImageFilter {
        -m_UseImageSpacing : bool
        -m_UseImageDirection : bool
        -m_OrderOfAccuracy : unsigned int
        +DynamicThreadedGenerateData()
        +GenerateInputRequestedRegion()
    }
    NeighborhoodOperator <|-- HigherOrderAccurateDerivativeOperator
    ImageToImageFilter <|-- HigherOrderAccurateDerivativeImageFilter
    ImageToImageFilter <|-- HigherOrderAccurateGradientImageFilter
    HigherOrderAccurateDerivativeImageFilter ..> HigherOrderAccurateDerivativeOperator : uses
    HigherOrderAccurateGradientImageFilter ..> HigherOrderAccurateDerivativeOperator : uses

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