Add lightweight experiment management and versioning

[novis10813]

Summary

Add basic experiment tracking to ResearchSession, allowing users to save/load experiments and track factor evolution over time.

Background

Factor research involves many iterations. Without experiment tracking, it's easy to lose track of what worked and what didn't. This provides a lightweight solution before full Knowledge Graph integration.

Goals

• Save experiment configurations and results
• Load and compare historical experiments
• Track factor performance over time

Proposed Tasks

• Add ResearchSession.save_experiment(name: str, output_dir: str) method
  • Saves factor definition, analysis results, backtest results
  • Creates timestamped directory with config.json
  • Reuses FactorAnalysisResult.save() structure
• Add ResearchSession.load_experiment(path: str) method
  • Loads experiment configuration
  • Returns Experiment object with metadata
• Add ResearchSession.list_experiments(output_dir: str) method
  • Lists all saved experiments
  • Returns summary (name, date, key metrics)
• Create simple SQLite-based experiment registry (optional, for faster querying)
• Add unit tests for experiment save/load
• Update documentation with examples

Notes

• Should integrate with existing FactorAnalysisResult.save() structure
• Keep it lightweight (file-based) - full Knowledge Graph comes later
• Consider experiment comparison utilities (diff two experiments)
• Should support both manual naming and auto-generated names