cookies: track expiration in jar to optimize removals

Removing expired cookies needs to be a fast operation since we want to
be able to perform it often and speculatively. By tracking the timestamp
of the next known expiration we can exit early in case the timestamp is
in the future.

Closes: #7172
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

lib/cookie.h

@@ -65,6 +65,7 @@ struct CookieInfo {
   bool running;    /* state info, for cookie adding information */
   bool newsession; /* new session, discard session cookies on load */
   int lastct;      /* last creation-time used in the jar */
+  curl_off_t next_expiration; /* the next time at which expiration happens */
 };
 
 /* This is the maximum line length we accept for a cookie line. RFC 2109