fix: work around asyncssh/fido2 AttributeError on Python 3.14 non-Windows

[Copilot]

On Python 3.14, ctypes.HRESULT was removed for non-Windows platforms. When fido2 is installed in the HA environment, asyncssh's sk.py attempts from fido2.client.windows import WindowsClient inside a try/except ImportError block — but fido2/client/win_api.py raises AttributeError at module level (HRESULT = ctypes.HRESULT), which goes uncaught and blows up the entire asyncssh import.

Fix

Pre-attempt the problematic import in coordinator.py before asyncssh is loaded. On failure, write None into sys.modules["fido2.client.windows"] — Python's negative-cache mechanism — so that asyncssh's subsequent import attempt raises ImportError instead, which it already handles gracefully (disabling Windows WebAuthn support).

if sys.platform != "win32":
    try:
        import fido2.client.windows  # noqa: F401
    except (ImportError, OSError, AttributeError) as _fido2_err:
        _LOGGER.debug(
            "fido2.client.windows unavailable (%s); asyncssh Windows WebAuthn support disabled",
            _fido2_err,
        )
        sys.modules["fido2.client.windows"] = None

This is a targeted workaround for a bug in asyncssh's exception handling (except ImportError should be except (ImportError, AttributeError)). No functional behaviour changes on Windows or in environments where fido2 is absent or fully compatible.