feat!: Add file-based environment variable support and migrate to Poetry

Summary

This MR introduces file-based environment variable support for secure secret management and modernizes the project build system by migrating from pip + setuptools to Poetry.

Changes

🚨 Breaking Changes

• File-based environment variables: _FILE suffixed environment variables are now automatically processed
  • When <VAR>_FILE is set, the system reads the file path and loads contents as <VAR>
  • Raises error if both <VAR> and <VAR>_FILE are defined simultaneously
  • Enables Docker secrets and Kubernetes mounted secrets workflows

Features

• Poetry migration: Replaced pip + setuptools with Poetry for dependency management
  • Modern dependency resolution and lock file support
  • Simplified build and publish workflows
  • Better development environment management

Improvements

• Enhanced documentation clarity and completeness
• Improved type hints throughout the codebase
• Better code maintainability and error handling
• Refined function signatures and docstrings