fix: Update canopy after Merkle tree updates (#934)

Before this change, we were updating canopy only after appends. Now
we do it also for updates.

Add unit tests which assert the whole canopy.

merkle-tree/concurrent/src/lib.rs

@@ -413,6 +413,10 @@ where
         }
         self.changelog.push(changelog_entry);
 
+        if self.canopy_depth > 0 {
+            self.update_canopy(self.changelog.last_index(), 1);
+        }
+
         Ok((self.changelog.last_index(), self.sequence_number()))
     }