Fix package names and mark build-dependent deps as optional

[AmelieLang]

Summary

• Fix finnhub -> finnhub-python: the original package name does not exist on PyPI and causes pip install to fail for all new users
• Mark torch>=2.0.0 as optional comment — saves ~2GB on default install
• Mark bt>=1.2.0 as optional comment — requires Microsoft C++ Build Tools to compile on Windows

Test plan

• pip install -r requirements.txt completes without errors on a clean Python 3.11+ environment
• import finnhub works after install
• Users who need bt or torch can install them separately