[WIP]feat: refactor the python code structure.

[jackfiled]

This pull request addresses the following issues:

• The Python code in the project is dispersed across different directories and is copied into the build directory by CMake, which makes debugging and running Python code difficult.

• The existence of both requirements.txt and pyproject.toml files in the root directory may cause confusion for new developers.

This pull request implements the following changes:

• Moves all Python source code into the src directory.

• Manages Python dependencies through the pyproject.toml file.

• Handles installation of Python code using Python package managers (pip, uv, etc.).

However, this pull request still requires additional work:

• Integration with the LLVM Python infrastructure as the mlir package from LLVM still needs to be referenced by PYTHONPATH environment variable.

• Documentation updates to align with the new development.