Inconsistent access to CLI info

[mccalluc]

It doesn't look like the end-to-end demo test actually exercises --demo:

In the tests:

app = App(
    app_ui,
    make_server_from_cli_info(
        CLIInfo(
            public_csv_path=None,
            private_csv_path=None,
            contributions=1,
            is_demo=True,
        )
    ),
)

def make_server_from_cli_info(cli_info: CLIInfo):
    def server(input: Inputs, output: Outputs, session: Session):  # pragma: no cover
        public_csv_path = reactive.value(  # noqa: F841 # TODO
            cli_info.public_csv_path or ""
        )
        private_csv_path = reactive.value(cli_info.private_csv_path or "")

        contributions = reactive.value(cli_info.contributions)

In contrast, in dataset_ui, the CLIInfo is coming from the environment, and it never sees our manual override:

def dataset_ui():
    cli_info = get_cli_info()

def get_cli_info() -> CLIInfo:  # pragma: no cover
    args = _get_args()
    if args.demo:
        return _get_demo_cli_info()

def _get_args():
    """
    >>> _get_args()
    Namespace(public_csv_path=None, private_csv_path=None, contributions=1, demo=False)
    """
    arg_parser = _get_arg_parser()

    if "pytest" in argv[0] or ("shiny" in argv[0] and "run" == argv[1]):
        # We are running a test,
        # and ARGV is polluted, so override:
        args = arg_parser.parse_args([])  # pragma: no cover
    else:
        # Normal parsing:
        args = arg_parser.parse_args()  # pragma: no cover

My guess is that we should get rid of all the special logic in UI code, and make sure the information flow is always from the server.