chore: raise npsim baseline to C++20 and modernize C++17-era target/code usage

[Copilot]

This updates the project to use C++20 as the minimum/default language level and removes remaining C++17 target requirements. It also applies a focused code-path simplification enabled by C++20 container APIs.

• Build standard policy

  • Set project default C++ standard to 20 in top-level CMake.
  • Tightened accepted override standards from 17|20|23 to 20|23.

• Target-level CMake requirements

  • Replaced cxx_std_17 with cxx_std_20 in:
    • src/geocad/CMakeLists.txt
    • src/tools/CMakeLists.txt
  • Keeps per-target declarations aligned with project-wide baseline.

• C++20 simplification in code

  • Simplified map lookup in TOCCToStep::GetLabelOfVolume using contains() + at() instead of find()/end() + indexed access.
  • This makes intent explicit and avoids implicit insertion semantics from operator[].

if (fTree.contains(v))
   return fTree.at(v);
return TDF_Label{};

[Copilot]

Pull request overview

Updates npsim’s build configuration and a small GeoCad code path to assume a C++20 baseline, removing remaining C++17 requirements and using C++20 container APIs where helpful.

Changes:

• Set project-wide default C++ standard to 20 and restrict allowed overrides to 20 or 23.
• Update per-target CMake cxx_std_* requirements from 17 → 20 in tools and GeoCad.
• Simplify TOCCToStep::GetLabelOfVolume using std::map::contains() + at().

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
CMakeLists.txt	Raises project default C++ standard to 20 and tightens accepted standard overrides.
src/tools/CMakeLists.txt	Updates tool executables’ target compile features to require C++20.
src/geocad/CMakeLists.txt	Updates GeoCad library target compile features to require C++20.
src/geocad/src/TOCCToStep.cxx	Uses C++20 contains()/at() for map lookup and avoids operator[].

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[github-actions]

Capybara summary for PR 51

• sim_dis_10x100_minQ2=1000_epic_craterlake
• sim_dis_10x100_minQ2=1_epic_craterlake
• sim_dis_18x275_minQ2=1000_epic_craterlake
• sim_dis_18x275_minQ2=1_epic_craterlake
• sim_dis_5x41_minQ2=1_epic_craterlake
• sim_e_1GeV_20GeV_epic_craterlake
• sim_pi_1GeV_20GeV_epic_craterlake
  ^{_{Last updated 2026-05-17T13:58-04:00 92ab8fa}}