Fix clang build: constexpr pi initialization

[Copilot]

constexpr double pi = std::acos(-1.0) is rejected by clang since std::acos is not constexpr there (GCC accepts it as an extension). This caused CI failures on all clang builds.

Fix

Changed constexpr → const in both affected files:

// Before (fails on clang)
constexpr double pi = std::acos(-1.0);

// After (portable)
const double pi = std::acos(-1.0);

• utils/Test/testDeproject.cc — anonymous namespace
• utils/Test/testEmpDeproj.cc — inside main

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[The9Cat]

Okay, let's try it.