feat: gen rand dbc id src from public address

src/dbc_id.rs

@@ -117,6 +117,16 @@ impl PublicAddress {
     pub fn new(public_key: PublicKey) -> Self {
         Self(public_key)
     }
+
+    /// A random derivation index and the public address.
+    /// The random index will be used to derive a DbcId out of the public address.
+    pub fn random_dbc_id_src(&self, rng: &mut impl RngCore) -> DbcIdSource {
+        DbcIdSource {
+            public_address: *self,
+            derivation_index: random_derivation_index(rng),
+        }
+    }
+
     /// Generate a new DbcId from provided DerivationIndex.
     /// This is supposed to be a unique identifier of a Dbc.
     /// A new Dbc id is generated by someone who wants to send tokens to the PublicAddress.