crypto: Add a TODO about SAS timing out.

matrix_sdk_crypto/src/verification/sas/sas_state.rs

@@ -90,6 +90,9 @@ impl Default for AcceptedProtocols {
     }
 }
 
+// TODO implement expiration of the verification flow using the timeouts defined
+// in the spec.
+
 /// A type level state machine modeling the Sas flow.
 ///
 /// This is the generic struc holding common data between the different states