fix: ensure publisher is cleaned up on error in submit_document

If pub.send() raises an exception, pub.stop() was never called,
leaking the publisher and its underlying connection.

Wrap the pub.start()/pub.send() calls in try/finally so pub.stop()
is always called, matching the existing pattern at lines 345-361.

Fixes #871

trustgraph-flow/trustgraph/librarian/service.py

@@ -418,14 +418,15 @@ class Processor(AsyncProcessor):
             self.pubsub, q, schema=schema
         )
 
-        await pub.start()
+        try:
+            await pub.start()
 
-        # FIXME: Time wait kludge?
-        await asyncio.sleep(1)
+            # FIXME: Time wait kludge?
+            await asyncio.sleep(1)
 
-        await pub.send(None, doc)
-
-        await pub.stop()
+            await pub.send(None, doc)
+        finally:
+            await pub.stop()
 
         logger.debug("Document submitted")