true if the session's timestamp is within the last maxAgeMs milliseconds,
otherwise false.
Remarks
A session is considered fresh if Date.now() - session.timestamp < maxAgeMs.
This is a simple age‑based heuristic; it does not validate the session against
the server.
Example
if (isSessionFresh(session, 3600000)) { console.log('Session is less than 1 hour old'); }
Checks if a cached session is still fresh based on its age.