[MAINTENANCE] Build system cleanup: remove unused libevent, consolidate dispatch scripts, fix version tracking

[yunlishao-vibe]

Task Summary

The build system has accumulated technical debt: libevent is vendored but marked "Not currently used", dispatch scripts have grown organically without consistency, RealSimVersion.h.in uses the old branding, and the generate_version.ps1 script is disconnected from the dispatch pipeline.

Why is this needed?

• CommonLib/libevent/ is a large vendored library (50+ headers) noted as "Not currently used" in dependencies.yaml — it should be removed from the repo or gated behind a proper optional flag
• dispatch.bat calls scripts numbered 1–7 but the scripts are numbered 1–7 with gaps and naming inconsistencies (e.g., 5a_carmaker_components.ps1 vs 4_virtual_environment.bat)
• scripts/generate_version.ps1 exists but is not called by dispatch.bat — version generation is a manual step
• RealSimVersion.h.in uses REALSIM_VERSION_* prefix (tracked in issue [MAINTENANCE] Unify RealSim→FIXS branding in source code, logs, and comments #128 for renaming, but the version generation script also needs updating)
• build_libsumo.ps1 and build_sumo_executables.ps1 are in scripts/ root but not integrated into dispatch.bat
• The dispatch.bat build log goes to scripts/dispatch/build.log but there's no CI artifact collection

Scope of Work

1. Remove libevent from CommonLib

• Remove CommonLib/libevent/ directory (50+ vendored headers, never used)
• Remove libevent from dependencies.yaml
• Remove libevent build from scripts/dispatch/1_external_libraries.bat
• Verify no source files include libevent headers (grep across all .cpp/.h)
• Add note to doc/BUILD.md about what libevent was and why removed

2. Fix dispatch script numbering and naming

• Renumber scripts for consistency: 1-external, 2-core, 3-vissim, 4-carmaker, 5-dspace, 6-mex, 7-virtualenv, 8-buildinfo
• Ensure dispatch.bat calls all scripts in correct order
• Integrate scripts/generate_version.ps1 into the dispatch pipeline (call before build)
• Document each script's purpose in doc/BUILD.md

3. Integrate libsumo build scripts

• Move scripts/build_libsumo.ps1 and scripts/build_sumo_executables.ps1 into scripts/dispatch/ or document them as standalone utilities
• Add them to BUILD.md with clear instructions on when to use them

4. Add auto-test

• Add tests/Python/test_build_system.py that validates:
  • No libevent headers are included in any source file
  • All dispatch scripts exist and are referenced in dispatch.bat
  • dependencies.yaml is valid YAML and contains required keys
  • RealSimVersion.h (generated) exists after build with expected macro names

5. Update .gitignore

• Ensure build/ output directory is properly gitignored (except prebuilt binaries intentionally committed)
• Add *.log for build log files in scripts/dispatch/

Files Involved

• CommonLib/libevent/ (delete)
• dependencies.yaml
• scripts/dispatch/*.bat, *.ps1
• scripts/dispatch/dispatch.bat
• scripts/generate_version.ps1
• scripts/build_libsumo.ps1, scripts/build_sumo_executables.ps1
• doc/BUILD.md
• .gitignore
• tests/Python/test_build_system.py (new)

Acceptance Criteria

• CommonLib/libevent/ removed from repo
• No source file includes libevent headers
• Dispatch scripts consistently numbered and all called from dispatch.bat
• generate_version.ps1 integrated into build pipeline
• tests/Python/test_build_system.py passes
• doc/BUILD.md updated to reflect changes

Branch and PR Target

• All PRs for this issue should target the dev branch (not main)
• First ensure main is merged into dev before starting work