feat(backend): tests v2

[KaliszS]

Closes #581

• tests will use testcontainers now instead of manual creating testing database
• factory-boy has been replaced with more modern factory library -> polyfactory
• more parametrizing to reduce code redundancy

[KaliszS]

Old tests directory (_tests) will be removed after the PR will be ready. Now they've stayed for a reference.

[bartmichalak]

@KaliszS is there any ongoing work here? Or are we good to review and merge after resolving the linter issues?

[KaliszS]

I will remove draft label as soon as it will be ready for review.

[bartmichalak]

tests will use testcontainers now instead of manual creating testing database

What will be the outcome?

[KaliszS]

tests will use testcontainers now instead of manual creating testing database

What will be the outcome?

Besides cleaner architecture, we won't need to create test database everytime we drop local postgres container. Right now, when I need to drop local db (for example because of migrations that neeed to be corrected), I have to enter pg container, run psql -U open-wearables and then create database open_wearables_test;. Using testcontainers will make it unnecessary.

We also have to structure tests differently to have a full control. Right now there is too much vibe coded code within that directory (we all have done that in the scope of many different pull requests).