Python 3.12 support

[nsoranzo]

Fix #625 .
Builds on #626 and rewrites src/past/translation/__init__.py to use importlib instead of imp when available.

Also:

• Fix several tests for recent Python versions.
• Drop some unused imports and functions.
• Add Python 3.8-3.12 classifiers.

[liquidsec]

Can we get some confirmation this project is actually still maintained? We are about to fork @nsoranzo's fork and hardcode that as a dependency in a large project because there are no signs of life.