[Feature] [Dubbo-python] Project standardization

[cnzakii]

What is the purpose of the change

ISSUE: #15063

Brief changelog

The pr aims to standardize the Dubbo Python project structure and code style based on the latest mainstream standards, as outlined by the Python Packaging Authority Packaging Guide and PEP 8 – Style Guide for Python Code. The main points of focus are:

1. The project structure will adopt the src layout.
2. Linting rules will follow mainstream rules like pycodestyle, pyflakes, and some additional specific rules.
3. We will adhere to PEP 518, gradually integrating various configuration files into pyproject.toml.
4. ...

Verifying this change

Checklist

• Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
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• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist.
• Add some description to dubbo-website project if you are requesting to add a feature.
• GitHub Actions works fine on your own branch.
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[cnzakii]

@AlbumenJ PTAL