pub fn is_valid_header_name(name: &str) -> bool
检查 Header 名是否合法（RFC 7230 token 定义）
token = 1tchar tchar = “!” / “#” / “$” / “%” / “&” / “’” / “” / “+” / “-” / “.” / “^” / “_” / “`” / “|” / “~” / DIGIT / ALPHA