This commit adds a new test file, `tests/test_cli.py`, containing
unit tests for the `_os_timezone` function in `netsleuth.cli`.
The tests cover:
- Happy paths (TZ variable, /etc/localtime symlink, /etc/timezone file)
- The edge case of an `OSError` exception being thrown when reading the
/etc/timezone file.
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
_default_gateway() took whichever 0.0.0.0 line route print printed first,
not the one Windows actually uses (lowest metric). With a VPN adapter
installed (Radmin VPN, Tailscale, ...) its default-ish route can print
before the real one. Verified live: was reporting Radmin VPN's 26.0.0.1
while Ethernet (the interface actually carrying traffic, confirmed via
primary_interface_ip()) has gateway 192.168.3.1; now reports that correctly.
Parsing extracted into pure _parse_windows_default_gateway(), tested against
a captured multi-adapter route print sample.
