Support for typing-extensions version 4 module

[nitishraghunathan]

The latest version of aiodynamo (as of cutoff 2021-09) supports typing-extensions version 3.10.0.2. However, there is an issue where the self type is not recognized. To address this, it would be beneficial to add support for typing-extensions version 4 or higher, as this version provides explicit typing support.

[ojii]

However, there is an issue where the self type is not recognized.

aiodynamo doesn't use this type, so why is this an issue?

To address this, it would be beneficial to add support for typing-extensions version 4 or higher, as this version provides explicit typing support.

Python 3.7, the reason we even have the (conditional) typing-extensions dependency, will reach EOL in about a month, so I think the better move forward would be to drop 3.7 support and remove the typing-extensions dependency altogether.

[y26805]

Since #161 removed support for Python 3.7, we can probably close this issue?
Also it looks like typing-extensions is required by mypy and black, and not something stated explicitly in our pyproject.toml.