COMP: Audit — disable all CTest warning suppressions to surface hidden warnings

[hjmjohnson]

Diagnostic PR: temporarily comments out every CTEST_CUSTOM_WARNING_EXCEPTION / CTEST_CUSTOM_ERROR_EXCEPTION pattern in CMake/CTestCustom.cmake.in so CI surfaces the warnings each suppression was hiding. Not intended to merge as-is — the goal is to read the CDash output and then restore only the suppressions that are still warranted.

Follow-up to the suppression-audit note on #449 (CTestCustom.cmake.in — "we should review all the suppressions and re-evaluate whether they are needed").

What to look at in CI

• CDash will likely show many warnings (third-party Modules/ThirdParty/..., vnl, OpenCV, Sphinx deprecations, etc.).
• CTEST_CUSTOM_MAXIMUM_NUMBER_OF_WARNINGS is still 199, so CDash truncates the list at 199 — the count is a floor, not the true total.
• The set() scaffolding and ${VAR} continuation lines are preserved, so the configured CTestCustom.cmake stays valid with an empty exception list.

Next steps

1. Categorize surfaced warnings: (a) third-party / vendored code we don't control → keep suppression; (b) our own examples/docs → fix at source; (c) stale patterns matching nothing → delete.
2. Restore suppressions in category (a), drop category (c), open fixes for category (b).

[hjmjohnson]

Diagnostic complete — closing. This PR intentionally disabled every CTestCustom.cmake.in suppression to surface what they were hiding; it was never meant to merge. The findings have been triaged into focused PRs.

What was discovered and where it was fixed

Surfaced by disabling suppressions	Outcome
itk::LabelGeometryImageFilter deprecation in GeometricPropertiesOfRegion (the only genuine compiler warning in our examples)	Fixed in #462 — migrated the example to LabelImageToShapeLabelMapFilter + LabelStatisticsImageFilter; its suppression removed
Broken sed -i "6559d" hack on Sphinx's cpp.py (edited an unrelated line; relied on removed distutils) and the Duplicate C++ declaration handling	Replaced in #463 + #464 with suppress_warnings = ['duplicate_declaration.cpp']
breathe parser-skip notices on a few complex ITK signatures it cannot parse	Targeted CTest exception added in #464
libpng sCAL (runtime), vnl, and other third-party warnings	Confirmed legitimate; suppressions kept

The C++ example builds themselves were clean on clang and gcc — the surfaced items were a single deprecated-API usage plus doc-toolchain and third-party noise. No code from this branch is needed.