fix: resolve tiktoken import error and update dependencies

- Add tiktoken and openai as optional dependencies to requirements.in
- Regenerate requirements.txt with proper hashes using pip-compile
- Fix tiktoken import error in OpenAISummarizer with proper type annotations
- Update pyproject.toml with openai optional dependency group
- Add installation instructions for OpenAI dependencies in README.md
- Ensure all dependencies are preserved with security hashes

Author: AlmostBald-TRADING