Add proper pytest support and guidelines in the Ruff config. #76
Description
Request
The current Ruff config is designed for the Python source code. It doesn't full fit the pytest requirements. We should look into pytest specific rules in Ruff and come up with a pytest oriented config.
Possible implementation
In Spider, we manually turned off the following rules to make it compatible with pytest: https://github.com/y-scope/spider/blob/1177a7fdacaa397edf8693bc475471a1fb793ccc/ruff.toml#L27
We can compile a formal rule set as the standardized pytest coding guideline.