Fix type error with newly created remote tags

And add some assertions to fail faster when there is type skew.

This hopefully addresses the following exception:

  Traceback (most recent call last):
    ...
    File ".../beets-ibroadcast/beetsplug/ibroadcast/command.py", line 77, in func
      self.upload(item, force=opts.force)
    File ".../beets-ibroadcast/beetsplug/ibroadcast/command.py", line 169, in upload
      self._sync_tags(trackid, item)
    File ".../beets-ibroadcast/beetsplug/ibroadcast/command.py", line 231, in _sync_tags
      self._update_tags(item, lastsync_tagids)
    File ".../beets-ibroadcast/beetsplug/ibroadcast/command.py", line 271, in _update_tags
      item.ib_tagids = '|'.join(tagids)
  TypeError: sequence item 0: expected str instance, int found

beetsplug/ibroadcast/command.py

@@ -113,6 +113,15 @@ def _stack_trace(self, e):
         if self._verbose():
             self.plugin._log.exception(e)
 
+    @staticmethod
+    def _assert_type(obj, expected_type):
+        assert type(obj) == expected_type
+
+    @staticmethod
+    def _assert_element_type(items, expected_type):
+        for item in items:
+            assert type(item) == expected_type
+
     @staticmethod
     def _trackid(item):
         return int(item.ib_trackid) if hasattr(item, 'ib_trackid') else None
@@ -193,6 +202,10 @@ def _sync_tags(self, trackid, item):
         remote_tagids = set(self._remote_tagids(trackid))
         lastsync_tagids = set(self._lastsync_tagids(item))
 
+        self._assert_element_type(local_tagids, str)
+        self._assert_element_type(remote_tagids, str)
+        self._assert_element_type(lastsync_tagids, str)
+
         locally_added = local_tagids - lastsync_tagids
         locally_removed = lastsync_tagids - local_tagids
         remotely_added = remote_tagids - lastsync_tagids
@@ -241,7 +254,7 @@ def _tagid(self, tagname):
         # New remote tag -- create it.
         self.plugin._log.debug(f"--> Creating remote tag '{tagname}'")
         try:
-            tagid = self.ib.createtag(tagname)
+            tagid = str(self.ib.createtag(tagname))
             self.ib.tags[tagid] = {'name': tagname}
             self.tags[tagname] = {'id': tagid}
             return tagid