fix(ext): cross-platform IS_UV_VENV check without grep subprocess

[Vimal Sahani (VimalN2005)]

Summary

Fixes pytest test collection failure on Windows by replacing the Unix grep subprocess call in IS_UV_VENV with cross-platform Python file inspection.

Problem

In packages/autogen-ext/tests/code_executors/test_commandline_code_executor.py, IS_UV_VENV was defined as:
python subprocess.run( ["grep", "-q", "^uv = ", os.path.join(venv_path, "pyvenv.cfg")], check=False, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, ).returncode == 0

On Windows environments where grep is not natively installed in PATH, running pytest fails immediately during collection at import time:
ext packages\autogen-ext\tests\code_executors\test_commandline_code_executor.py:38: in <lambda> subprocess.run( ... FileNotFoundError: [WinError 2] The system cannot find the file specified

Solution

Replaced the external grep invocation with native Python file reading via Path.read_text():
`python
def _check_is_uv_venv() -> bool:
venv_path = os.environ.get("VIRTUAL_ENV")
if not venv_path:
return False
cfg_path = Path(venv_path) / "pyvenv.cfg"
if not cfg_path.is_file():
return False
try:
content = cfg_path.read_text(encoding="utf-8", errors="ignore")
return any(line.startswith("uv = ") for line in content.splitlines())
except OSError:
return False

IS_UV_VENV: bool = _check_is_uv_venv()
`

Benefits

1. Cross-Platform: Operates identically across Windows, macOS, and Linux without depending on shell utilities.
2. Performance: Avoids spawning an external process during pytest test collection.
3. Robustness: Gracefully handles missing pyvenv.cfg or OS permissions.

Testing

• Verified with uv run pytest packages/autogen-ext/tests/code_executors/test_commandline_code_executor.py on Windows (Python 3.12). Test collection succeeds and tests execute cleanly.
• Formatted and linted with uv run ruff check and uv run ruff format.