Fix OKX spot symbol bootstrap

[sklarsa]

Summary

• keep cryptofeed pinned to the existing locked dependency set
• add an OKXSpot subclass that only loads OKX SPOT instrument metadata for this spot-trades demo
• remove package-mode from pyproject so Poetry 1.3 can parse the project config

Testing

• poetry check
• poetry run python -m py_compile demo_questdb.py
• poetry run python -c "from demo_questdb import OKXSpot; print(OKXSpot.name)"
• git diff --check