Need tests for core functionalities

[qin-yu]

There has been a folder of tests, which inspired me to write tests for the model zoo module. Additionally, I observed some inconsistencies in the tests for the zarr module and revamped them. Let's keep up the momentum!

Core Functionalities

By core functionalities, I refer to everything available in the Napari GUI and its headless mode. Although there are overlapping functionalities and modules from the Legacy GUI/CLI, our focus should be on Napari and Headless for PlantSeg 2.0.

Code Coverage and Testing

Setting up Codecov to monitor every PR might be excessive at this stage. However, we still need to maintain awareness of our test coverage, and identify the current gaps in our tests. Is there an automated way to determine the missing tests?

Modules

Feel free to expand and organize the list of areas needing tests:

• [x] Preprocessing -> Image Rescaling #258