fix(mcconfigurator): Fix to run without TGeant3

[karabowi]

The MCConfigurator required TGeant3 and TGeant4 to run. Added compiler flags to enable running without any given transport engine.

Fixes issue #1620.

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Checklist:

• [x] Followed the Contributing Guidelines

[coderabbitai[bot]]

📝 Walkthrough

Walkthrough

The PR refactors mcconfigurator's build dependencies and optional feature support. It decouples mcconfigurator from hard-coded Geant3/Geant4/FastSim requirements by making these dependencies optional and detectable at compile-time via preprocessor macros. mcconfigurator now builds with only yaml-cpp present, while Geant3/Geant4/FastSim support is conditionally compiled when available.

Changes

Cohort / File(s)	Summary
Build configuration—dependency loosening fairroot/CMakeLists.txt	Changed mcconfigurator add_subdirectory condition from (Geant3_FOUND AND Geant4VMC_FOUND AND yaml-cpp_FOUND AND TARGET FairRoot::FastSim) to (yaml-cpp_FOUND), decoupling from Geant/FastSim hard requirements.
Build configuration—feature flags and linkage fairroot/mcconfigurator/CMakeLists.txt	Added public compile definitions (FAIRROOT_HAS_GEANT3, FAIRROOT_HAS_GEANT4, FAIRROOT_HAS_FASTSIM) when respective components are found; converted private linkage of geant321, geant4vmc, and FairRoot::FastSim to conditional public linkage; added EXTRA_INCLUDE_DIRS to ROOT dictionary target; updated copyright year.
CMake reorganization examples/CMakeLists.txt	Updated copyright year (2014-2022 → 2014-2025); moved add_subdirectory(common/gconfig) from inside Geant3_FOUND conditional to unconditional pre-check (gated on MCConfigurator).
Conditional compilation implementation fairroot/mcconfigurator/FairYamlVMCConfig.cxx	Replaced unconditional includes of FairFastSimRunConfiguration.h, TGeant3.h, TGeant3TGeo.h, and TGeant4.h with #ifdef-guarded includes (FAIRROOT_HAS_*); wrapped SetupPostInit(), SetupGeant3(), and SetupGeant4() implementations with feature guards; added fatal error messages when required features are unavailable; refactored Geant4 setup to conditionally build FastSim TG4RunConfiguration.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20–25 minutes

• fairroot/CMakeLists.txt: Verify that loosening the mcconfigurator condition from four requirements to one does not break supported build scenarios; ensure this aligns with downstream consumers.
• fairroot/mcconfigurator/CMakeLists.txt: Confirm all three conditional PUBLIC link targets and their guards are correctly paired with the new compile definitions.
• FairYamlVMCConfig.cxx: Cross-check that all #ifdef preprocessor guards in the source file match the corresponding compile definition conditions in CMakeLists.txt; verify fatal error messages are user-friendly and direct users to rebuild with required support.
• Integration: Ensure the interplay between loosened build conditions and conditional compilation guards allows graceful degradation when optional components are absent.

Possibly related PRs

• FairRootGroup/FairRoot#1611: Directly related—both PRs modify fairroot/CMakeLists.txt to decouple component inclusion from hard Geant3 requirements by moving or conditional-checking the mcconfigurator addition.

Suggested reviewers

• ChristianTackeGSI

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding support for running MCConfigurator without TGeant3, which is the core focus of the changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining that compiler flags were added to enable running without transport engines and referencing the corresponding issue.

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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