Document current code and propose project organization improvements

[Copilot]

This PR addresses the request to document the current codebase and propose improved project organization for rebayes-mini. The changes transform the repository from a functional but minimally documented package into a well-structured, user-friendly library while maintaining its minimalist philosophy.

Key Improvements

📚 Comprehensive Documentation

• Enhanced README: Added detailed project overview, installation instructions with dependencies, quick start guide, and feature descriptions
• API Reference: Complete documentation of all modules, classes, and functions in docs/api.md
• Developer Guide: Comprehensive contribution guidelines, coding standards, and development workflow in docs/developer.md
• Module Documentation: Added detailed docstrings and module-level documentation for all core components

🏗️ Improved Package Structure

• Package Initialization: Enhanced __init__.py files with proper imports, version info, and usage examples
• Module Documentation: Added comprehensive docstrings to states.py, callbacks.py, and methods package
• Clear Interfaces: Documented the 14 different filter implementations and their purposes
• Type Safety: Leveraged existing chex dataclasses with improved documentation

💡 Practical Examples

• Basic Kalman Filter: Complete working example with synthetic data generation and error analysis
• Robust Filtering: Comparison between standard and robust filters handling contaminated data
• Example Documentation: Clear instructions for running examples and understanding outputs

🎯 Project Organization Proposal

• Current State Analysis: Documented existing strengths and areas for improvement
• Future Roadmap: Proposed structure for tests, utilities, advanced examples, and CI/CD
• Implementation Phases: Prioritized roadmap for continued development

What's Included

The repository now provides:

For Users:

• Clear entry points with README and examples
• Comprehensive API documentation covering all 14 filter types
• Progressive learning path from basic to advanced usage

For Developers:

• Detailed contribution guidelines and coding standards
• Consistent project structure and interfaces
• Extensible design for adding new filters

For Maintainers:

• Reduced support burden through comprehensive documentation
• Professional appearance to attract contributors
• Clear roadmap for future enhancements

Validation

All changes have been validated to ensure:

• ✅ Core package imports work correctly
• ✅ JAX compatibility is maintained
• ✅ Basic functionality (states, callbacks) operates as expected
• ✅ Documentation examples are accurate and functional

The improvements maintain backward compatibility while significantly enhancing the user and developer experience. The minimalist core philosophy is preserved while providing the documentation and examples needed for broader adoption.

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