async def read_file(filename: str) -> str | None:
    """Read the contents of the given file as a string, asynchronously. File can be a
    local file or a remote file."""
    try:
        raw_contents = await read_single_async(filename)
    except FileNotFoundError:
        return None
    lines = []
    for line in raw_contents.decode("utf-8").split("\n"):
        if len(line) > 0:
            lines.append(line)
    assert len(lines) == 1, filename
    return lines[0]
Read the contents of the given file as a string, asynchronously. File can be a
    local file or a remote file.
neuron_explainer/explanations/explanations.py