feat: repo improvement suggestions

[comilao]

What 💻

This PR tries to make some improvement suggestions to this project based on Python Best Practices for a New Project in 2021 and my Python experience with this blog article.

There is only one additional dev dependencies introduced pre-commit, it can be installed into Git Hooks and run automatically before any git commit locally. Its configuration file is .pre-commit-config.yaml, and I have configured some hooks such as no trailing-whitespace and add new line at the end of file. Other hooks are isort, flake8, black, mypy. These hooks are installed by pre-commit at a separate location on the machine and will not interfere with dependency of this repo.

• isort groups imports into 3 categories, packages imported from Python own library, external library (web3) and other local imports. Within each category, it sorts imports in alphabetical order.
• flake8 is a linter, it can detect things like unused imports, variables; variable use before its creation and etc
• black is a formatter
• mypy is a static type checker for Python

Currently, within .pre-commit-config.yaml, it does not check any files, you can learn more about the exclude regex here. With refactor going on, we can change the exclude part and check those files slowly.

I would also like to explain some changes in this commit:
validate.yml will be using pre-commit to do a comprehensive check. ref
pyproject.toml has configs for isort and black. (NOTE: I personally prefers line length 99, as nowadays computer screen is quite wide, but if you don't like it, I can change it to the default 88)
setup.cfg has configs for flake8 and mypy, mypy config ref

Why ✋

When I first start to use this repo, I noticed the Any type is returned everywhere, mainly because of #63 , it made the developing experience very bad. Then I dig deeper, and noticed many unused imports, wrong type hints, and some wrong typing issue that could be caught with a linter. I would like to propose my Python practice to this repo. The better this repo is, the smoother my developing experience will be.

Evidence 📷

Include screenshots, screen recordings, or console output here demonstrating that your changes work as intended

Notes 📝

• Any notes/thoughts that the reviewers should know prior to reviewing the code?
  Sorry for this long PR, basically I would like to try my best to make this repo better, I finally found an open-source project that I feel I can contribute a lot.

• If you are okay with these changes, I can also edit the CONTRIBUTING.md with a notes on pre-commit hook installation and usage.
• BTW, if you accepted this PR, I can help to do the refactoring work with some minor parts in the repo first, such as zksync2/account, zksync2/core, zksync/manage_contracts, zksync/signer and zksync/transaction. I am thinking of using existing test cases to check the correctness of the refactoring and add more test cases accordingly.