fix install build file lack

[jikunshang]

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

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Purpose

we will always use develop install in ci to avoid python local first issue which may have conflicts in system path and delveop path for run pytest
update doc about build steps: prefer using pip install . instead of python setup.py install

Test Plan

Test Result

(Optional) Documentation Update

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[Copilot]

Pull Request Overview

This PR fixes a packaging issue where files in the vllm_xpu_kernels folder were not being included in the package distribution. The fix involves switching from automatic package discovery to explicit package specification and adding auto-imports for compiled extensions.

• Switches from setuptools.packages.find to explicit packages configuration
• Adds automatic imports for compiled C extensions (_C, _moe_C, _vllm_fa2_C, _xpu_C) in the package's __init__.py

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pyproject.toml	Changes package discovery from find configuration to explicit packages list
vllm_xpu_kernels/init.py	Adds imports for compiled C extension modules

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[Copilot]

The explicit packages configuration may not include subdirectories or subpackages within vllm_xpu_kernels. Consider using find_packages() or explicitly listing all subpackages if they exist, or use packages = {"vllm_xpu_kernels": "vllm_xpu_kernels"} with include-package-data = true to ensure all necessary files are included.

Suggested change

	packages = ["vllm_xpu_kernels"]
	packages = "find:"
	include-package-data = true

[baodii]

LGTM