feat: preparing for next major release

[aliev]

• [x] Remove unnecessary generics.
• [ ] Add replace setup.py and setup.cfg with pyproject.toml.
• [x] Support python versions >= 3.9.
• [x] Update pre-commit hooks.
• [x] Add DEBUG setting.
• [x] Add default type Any to UserType to make all generics that use it optional.
• [x] Segregate storages.
• [ ] Add examples.

[codecov-commenter]

:warning: Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 91.44737% with 13 lines in your changes missing coverage. Please review.

Project coverage is 93.42%. Comparing base (533d8d8) to head (09998b0).

Files with missing lines	Patch %	Lines
aioauth/oidc/core/grant_type.py	0.00%	7 Missing :warning:
aioauth/grant_type.py	87.87%	3 Missing and 1 partial :warning:
aioauth/server.py	90.47%	2 Missing :warning:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #104 +/- ## ========================================== - Coverage 94.49% 93.42% -1.07% ========================================== Files 17 17 Lines 763 761 -2 Branches 112 88 -24 ========================================== - Hits 721 711 -10 - Misses 33 37 +4 - Partials 9 13 +4 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.