perf: Add a quick test to measure ssb.following performance.

src/tests.c

@@ -1080,6 +1080,7 @@ void tf_tests(const tf_test_options_t* options)
 	_tf_test_run(options, "invite", tf_ssb_test_invite, false);
 	_tf_test_run(options, "triggers", tf_ssb_test_triggers, false);
 	_tf_test_run(options, "cli", tf_ssb_test_cli, false);
+	_tf_test_run(options, "following_perf", tf_ssb_test_following_perf, true);
 	tf_printf("Tests completed.\n");
 #endif
 }