Audit existing File class implementations

## 📋 What to do
Analyze all existing File classes and their differences.

## ✅ Tasks
- [ ] Review `File` in core/pireal_file.py
- [ ] Review `pfile.File` in core/_pfile.py  
- [ ] Review `file_manager.py`
- [ ] Document differences and usage

## 📝 Deliverable
Comment with analysis of the 3 implementations.