Entropy of initialisation vector

Make sure that the iv which is used in each message sent from Bisq has 32 bit of entropy.

In bisq/notification/BisqNotification.java, line 46, we use:
String iv = uuid.substring(0, 16);
which provides only 16+8 = 24 bit of entropy.

Start in bisq/notification/BisqNotification.java at line 46 and inspect how the UUID-derived IV is generated and used for each message. Verify the resulting IV provides 32 bits of entropy and confirm that each sent message uses the corrected value.

Written by the indexing model from the issue text.