fix: guard darwin network test import behind platform check

[Denay2468]

Problem

Running uv run pytest tests/ on Windows fails at collection time:

ModuleNotFoundError: No module named 'CoreWLAN'

pytestmark skips test execution but cannot prevent the top-level
import from running on Windows where CoreWLAN does not exist.
This crashes the entire test suite before any test runs.

Fix

Wrapped the import in if sys.platform == 'darwin' so it never
executes on Windows or Linux.

Before / After

Before: ERROR collecting tests/network_manager/test_darwin.py
After: 11 darwin tests skip cleanly on Windows

Tested on

• Windows 11 ✅

[Denay2468]

All checks passing. Fixed CRLF -> LF line endings. Ready for review!