Support for modern Python versions

[danfimov]

Are there any plans to support Python 3.12/3.13, etc.?
Additionally, the package could drop support for the EOL Python 3.8 version.

I conducted some research on the amount of work required, and here are my findings:

• The library's code can remain unchanged, as there are no blockers on this side.
• The aiomisc version used in this project seems outdated (it doesn't support Python 3.12, and I can reproduce an error related to the missing pkg_resources package locally - similar to that issue). However, we can update it to a newer version and install the aiomisc-pytest plugin separately.
• It seems that asyncpg declared support for Python 3.13 in version 0.30.0. However, it is still not listed in the project tags on PyPI, so pip cannot find a suitable version. This will likely be resolved in this issue. For now, we can add support for Python 3.12 and drop support for Python 3.8, while waiting for the asyncpg maintainers to fix this.
• pylama does not work with Python >3.10 as I see. We could replace it with ruff or another similar tool.

[danfimov]

I created PR for this issue #18

Code there will probably be corrected or split into several small PR after discussing what edits are really needed.