README.md update
modifications to simulation algorithm
Refactor project structure: introduce lib/ directory for non-executable core physics submodules and update package imports
Restructure project layout: replace pdg with physics_base, clean deprecated files, fix mkdocstrings bindings, and integrate master electron cross-sections plot
photon x-sections block created and described
Add gitignore, integrate relaxation visualization script and documentation updates
feat: add main simulation cascade loop template to geim.py
refactor: rename project files to improve architecture clarity