Returns a string representation of the client info suitable for inclusion in HTTP headers. Key/value pairs are formatted as "key/value" and joined by spaces in the order they were inserted.
Returns a new ClientInfo with the given items appended. Accepts either individual key/value pairs or another ClientInfo whose segments are merged in order. The original is not modified; mixing the two forms in a single call is supported.
Keys and values on pair arguments must contain only alphanumeric
characters plus _, ., +, or -. Exact key+value duplicates are
silently ignored. On error, an exception is thrown (all-or-nothing).
ClientInfo is an immutable, ordered list of key/value segments. Use ClientInfo.with to derive new values with additional segments.