fix: use importlib to load scripts/generate_pyi.py instead of package…

[Mikezhang001]

Hi, I ran into an install issue and this PR fixes it.

What happened

Fresh clone + ./install.sh blows up with:

ModuleNotFoundError: No module named 'scripts.generate_pyi'

The root cause is that setup.py does from scripts.generate_pyi import generate_pyi_file at the top level, but scripts/ doesn't have an __init__.py — so Python doesn't recognize it as a package.

Looks like this was introduced in #231 when generate_pyi.py was added to scripts/.

How to reproduce

git clone --recursive https://github.com/deepseek-ai/DeepGEMM.git
cd DeepGEMM
./install.sh   # boom

What I changed

Instead of adding a __init__.py to scripts/ (which feels wrong since it's not really a package), I moved the import into CustomBuildPy.generate_pyi_file() and used importlib to load it by file path:

import importlib.util
spec = importlib.util.spec_from_file_location(
    'generate_pyi', os.path.join(current_dir, 'scripts', 'generate_pyi.py')
)
mod = importlib.util.module_from_spec(spec)
spec.loader.exec_module(mod)
mod.generate_pyi_file(name='_C', root='./csrc', output_dir='./stubs')

This way scripts/ stays as a plain utility directory and the import only happens at build time when it's actually needed.

Tested locally, ./install.sh works fine after the change.