Add pytest testing

[rockerBOO]

To test certain features to speed up iteration and confidence in changes.

• Test get_optimizer()
• Add github action to run tests
• Bump typos action to latest

Example with tests running: rockerBOO#5

[kohya-ss]

Thank you for this! This is really cool. I'd like to add more tests in the future.

[FurkanGozukara]

awesome