Function parse_initial_payload 

pub fn parse_initial_payload(
    payload_str: Option<&str>,
    payload_file: Option<&Path>,
) -> Result<JsonValue, CliError>

解析初始 payload

优先级：--payload 字符串 > --payload-file 文件 > 默认空对象 {}

错误

• InvalidPayload：JSON 解析失败