Refactor: Use static version parsing in setup.py

[RinZ27]

Parsing the version string using exec() during package setup introduces unnecessary runtime dependencies and potential side effects. While functional, a more resilient and idiomatic approach involves static extraction of the version attribute from dj_rest_auth/__version__.py without code execution.

Implementing a regex-based search for the __version__ variable ensures the setup process remains focused and secure across different environments. This refactoring aligns with modern Python packaging standards and eliminates the risk associated with dynamic evaluation of external files during installation.

[iMerica]

This changes many things which are outside the scope of the intent defined in the PR title/summary.

[RinZ27]

@iMerica My apologies for the noise in the initial commit. I've just reverted the unrelated changes to setup.py (dependency versions, classifiers, etc.) and kept only the static version parsing via regex as originally intended. Also verified that the install_requires and other metadata now match the master branch exactly. Thanks for catching that.