Proposal to Add Type Hints

**Describe the solution you'd like**
I'd like to propose adding type hints to the `Aiokafka` project. I've used `mypy` to analyze the codebase, and I believe that adding type hints could significantly improve the code's readability, maintainability, and robustness.

result for mypy
``` shell
Found 2475 errors in 109 files (checked 133 source files)
```
By adding type hints, developers can better understand function signatures and catch potential bugs early in the development process. Additionally, it can make it easier for newcomers to contribute to the project and for existing contributors to navigate the codebase.

I'm willing to contribute to this effort if the maintainers are interested in pursuing it. Adding type hints could be a valuable enhancement to the Aiokafka project.

I can start with [aiokafka/consumer/consumer.py](https://github.com/aio-libs/aiokafka/tree/master/aiokafka/consumer) and fix all issue in this file first and continue with other files in another PR's or you can assign others to contribute