Add comprehensive documentation to generators/common.py

Added detailed comments and documentation throughout:

Module-level:
- Module docstring explaining purpose and capabilities
- Section headers for major functional groups
- Constant documentation

Class-level:
- Comprehensive TopologyCreator class docstring
- Detailed explanation of the five major functional areas
- Attribute documentation

Method-level:
- Enhanced docstrings for all major methods
- Explanation of algorithms and strategies
- Parameter and return value documentation
- Example outputs where helpful

Inline comments:
- Complex logic explanations (rack assignment, interface expansion)
- Helper function documentation
- Strategy explanations (middle rack calculation, device positioning)

Section headers added for:
- Utility functions
- Internal helper methods
- Data loading and preparation
- Location and site creation
- IP address and number pool management
- Device creation
- Connectivity and cabling

This improves code maintainability and helps developers understand
the topology generation workflow.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: petercrocker