Add Round Robin and Least Connections load balancing algorithms

[Om-Nejakar]

Fixes issue:
Closes #6822

Changes:

• Added a new C++ file networking/src/load_balancing.cpp.
• Implemented two load-balancing algorithms:
  1. Round Robin (index rotation using modulo)
  2. Least Connections (linear scan over vector)
• Included a small main() demonstrating usage of both algorithms and expected output.
• Added basic input-safety checks (handle empty server list / empty connections).