Adds dry-python/returns

[sobolevn]

Link: https://github.com/dry-python/returns Docs: https://returns.readthedocs.io/en/latest/pages/future.html

What is this project?

This project is a collection of primitives for typed functional programming. Among others we have Future, FutureResult, and ReaderFutureResult monads.

You can also write your own implementation using Higher Kinded Types and our existing interfaces.

Why is it awesome?

• The only typed functional async programming library I am aware of
• Well documented and well tested
• Supports any IO loop, not just asyncio, tested with anyio
• Provides interfaces and Higher Kinded Types to implement your own solution if you need to