Remove python 3.8 deprecation / unsupported FFs and cleanup tests

[amazimbe]

What are you trying to accomplish?

In order to support the smooth deprecation of python 3.8 we added two feature flags: python_3_8_deprecation_warning and python_3_8_unsupported_error. As we stopped supporting python 3.8 on 5th February 2025, these feature flags are no longer required and this PR removes them to make the code easier to maintain.

How will you know you've accomplished your goal?

After this PR is merged, the feature flags python_3_8_deprecation_warning and python_3_8_unsupported_error will be removed from the codebase and tests should continue to pass.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.