Use ThreadPoolExecutor instead of Bare Threads

[rabinadk1]

1. Use ThreadPoolExecutor to make threads automatically join the calling thread
2. Use it to join hanging threads
3. Use staticmethod instead of classmethod when the class variable is not used
4. Use thread lock as a context manager
5. Remove unused parameter id
6. Formatted the code using black
7. Sorted imports with isort
8. Resolved flake8 errors
9. Write a definite version in requirements.txt