feat: Support local testing for Python

[frostming]

This PR adds support for Python local testing

How it works

• Creates a virtualenv in initialization stage, install pytest into it. I've considered using the standard lib unittest, but I can't implement the test matrix as easy as pytest.
• Generate a conftest.py once to parametrize the test cases according to the input and output values

TODO

• [x] System design questions
• [x] Robust input & output conversion
• [ ] Data structure deserialization

[j178]

Thanks for your contribution, very impressive (as always)!

One thing left is that we need to do parameter deserialisation before calling the solution function, since there are questions whose input is list, ListNode or TreeNode.

Maybe we need to wait for the determination of #112 first.

[frostming]

One thing left is that we need to do parameter deserialisation before calling the solution function, since there are questions whose input is list, ListNode or TreeNode.

Yeah, it will make the code grow, may be better to extract it to a python package, as go does.