COMP: Add ITKZLIB private dependency to ITKReview

[hjmjohnson]

Fixes the libITKReview shared-library link failure (undefined _itkzlib_gz* symbols) seen in ITKSphinxExamples python-superbuild CI by adding ITKZLIB to the module's PRIVATE_DEPENDS.

Root cause and verification

itkVoxBoCUBImageIO.cxx includes itk_zlib.h and calls itkzlib_gzopen/gzread/gzwrite/..., but ada67f6 ("COMP: Update ITKReview depends and linkage") moved all module dependencies except ITKIOImageBase to COMPILE_DEPENDS, dropping zlib from the link closure. ITKZLIB was never declared in either list.

The failure only manifests in BUILD_SHARED_LIBS=ON builds (e.g. Python wrapping), which is why ITK's own static-build CI stayed green. First observed in ITKSphinxExamples CI:
https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/actions/runs/27319825769/job/80794743298

Reproduced and fix verified locally on macOS arm64 (AppleClang, Release, shared libs, Module_ITKReview=ON, ITK_BUILD_DEFAULT_MODULES=ON, ITK_LEGACY_REMOVE=ON): link succeeds and otool -L shows @rpath/libitkzlib-6.0.1.dylib.

PRIVATE_DEPENDS matches the pattern used by ITKIOVTK and ITKIOGIPL, since zlib is referenced only from the .cxx, not from module headers.

[hjmjohnson]

Audited all of ITK for further instances of this issue: ITKReview was the only link-breaking case. A second, compile-time-only gap in Montage is fixed in the follow-up commit.

Audit method and findings

Scanned every non-ThirdParty module's src/ and include/ for includes of vendored third-party headers (itk_zlib.h, itk_png.h, itk_tiff.h, itk_jpeg.h, itk_expat.h, itk_hdf5.h, itk_minc2.h, itk_eigen.h) and cross-checked each hit against the declarations in that module's itk-module.cmake.

Module	Header	Declared?	Severity
Nonunit/Review	itk_zlib.h	no	Link failure in shared builds — fixed by commit 1
Registration/Montage	itk_eigen.h (in public itkTileMontage.hxx)	no	Compile-time only — fixed by commit 2

All other modules declare their third-party dependencies correctly.

Rationale for the Montage commit: Eigen is header-only, so the missing declaration cannot cause a link failure; Montage currently compiles only because ITKEigen3's include path arrives transitively through ITKCommon's dependency chain. That is the same fragile transitive reliance that broke ITKReview, so it is declared explicitly (COMPILE_DEPENDS, since no symbols are linked) for completeness. Verified locally: full build with Module_Montage=ON succeeds.

[blowekamp]

Please just simplify/correct the added documentation for COMPILE_DEPENDS.

[blowekamp]

LGTM. Thank for updating the sphinx examples too!