[build]: flatten ktransformers package shim

[JimmyPeilinLi]

Message:

Flatten the minimal top-level ktransformers import shim from a package directory to a single ktransformers.py module.

Scope:

• Move ktransformers/__init__.py to ktransformers.py.
• Switch setuptools packaging from packages = ["ktransformers"] to py-modules = ["ktransformers"].
• Keep the existing ktransformers distribution metadata and dependency/extras logic unchanged.

Why:

• Avoid keeping a root-level ktransformers/ source directory next to kt-kernel/.
• Preserve pip install ktransformers and import ktransformers behavior.

Validation:

• Built the top-level ktransformers wheel locally on sapphire4 from commit d143cf3.
• Verified wheel contents contain ktransformers.py and no ktransformers/ package directory.
• Verified METADATA keeps kt-kernel==0.6.1, [sft], and [sglang] dependencies.
• Installed the wheel into a clean local venv with --no-deps and verified import ktransformers, __version__ == 0.6.1, distribution version 0.6.1, and hasattr(ktransformers, "__path__") == False.
• No PyPI publish.

[gemini-code-assist]

Code Review

This pull request updates the project structure by changing the top-level package to a module and updating the build configuration in pyproject.toml. Additionally, it improves the version reading logic in ktransformers.py. I have reviewed the changes and suggest explicitly specifying the encoding when reading the version file to ensure cross-platform compatibility.

[gemini-code-assist]

It is recommended to specify an encoding (e.g., encoding="utf-8") when calling read_text(). This ensures consistent behavior across different platforms and locales, especially on Windows where the default system encoding might not be UTF-8, potentially leading to issues if the file contains non-ASCII characters.

Suggested change

	exec(version_file.read_text(), ns)
	exec(version_file.read_text(encoding="utf-8"), ns)