COMP: Suppress Eigen3 shadow warnings in CDash reports

[blowekamp]

Description

This PR addresses shadow warnings from the third-party Eigen3 library that appear in CDash build reports.

Changes

• Added CTest warning suppression for Modules/ThirdParty/Eigen3 warnings
• Specifically targets shadow warnings like [-Wshadow-uncaptured-local] from Eigen's GenericPacketMath.h

Background

The warnings originate from Eigen 3.4.90 in lines like:

// GenericPacketMath.h:655 - lambda parameter 'a' shadows function parameter 'a'
return pminmax_impl<NaNPropagation, IsInteger>::run(a, b, 
  EIGEN_BINARY_OP_NAN_PROPAGATION(Packet, (pmin<Packet>)));

These are third-party library warnings outside ITK's control and should be suppressed to reduce noise in build reports while maintaining strict warning standards for ITK's own code.

Testing

• Follows existing pattern of suppressing third-party warnings in CTestCustom.cmake.in
• No functional changes to ITK code

[seanm]

I've already fixed this warning upstream BTW, so we could also just update our eigen.

eigen being header-only makes things trickier since you'll often get warnings ultimately from it, but in your own source files.

[dzenanz]

LGTM. Fixing warnings upstream is welcome, but it is only a temporary fix. New warnings are bound to appear over time.

[blowekamp]

Updating from upstreams is a preferred solution.