[test] reorganize tests related to zero/gemini

[ver217]

Overview

As we have already updated the folder structure of zero/gemini, we should also update tests folder structure.

Possible structure:

tests
| --- test_zero
       | --- test_gemini
       | --- test_legacy
       | --- test_low_level

Wanna track the development progress? Take a look at

proposal: #3410

Goal

Reorganize tests related to zero/gemini and ensure the CI can pass.