Upgrade to Poetry build system for dependency management

[dartt0n]

The current project relies on requirements.txt to manage dependencies, with versions strictly fixed up to the minor version, which is considered a bad practice. This is because other users will not be able to install this package due to version conflicts.

I suggest switching to using Poetry as a build system, that offers several advantages that can significantly improve development workflow and project maintainability by solving transitive dependencies problem.

I have also noted that the code in some areas is not well-formatted. I fixed that using black.

Please review the changes and provide your feedback on them.

[dartt0n]

Also, please notice, I have added myself to the package contributors: https://github.com/allseeteam/yandexgpt-python/blob/87e36c047dd412ec2cdf85949bdb2c3a28383efe/pyproject.toml#L9

Let me know, if you are okay with that