[phine-richiB]

Changelog 

[Changed]:

• Restructured demo and demo_containerized folders — core network configs (OAI, free5GC, Open5GS) moved to shared core_network_setup at repo root
• Updated OAI gNB and UE to v2026.w04
• Power plugins now target only the 2026 OAI version
• Switched from regex-based config modification to yaml-cpp for field substitution in plugins
• Restructured integration tests to match new folder layout

[Added]:

• Dynamic Gazebo world selection based on CORE_NETWORK environment variable (no manual editing or image rebuild needed)
• nvidia-container-toolkit optional requirement documented in demo_containerized README

[Fixed]:

• Applied clang-format to all plugin source files (aux_functions.cc, aux_functions.hh, gNBPowerPlugin.cc)
• Updated READMEs for both demo and demo_containerized with current instructions

Checklist

•  Code is tested and passes locally
•  Documentation is updated if needed
•  Follows code style and guidelines [Lint, Guidelines and co will follow if not existing]