fix(weave): keep traced_generator on calls_query_stream

Extracting _build_calls_query took the decorator with it, so the span named
calls_query_stream wrapped a plain function returning a tuple while the actual
generator -- a public API read path -- lost its span entirely. It went unnoticed
because unpacking cq, settings works on any iterable, including the generator
the decorator returned.

Author: nikumar1206

weave/trace_server/clickhouse_trace_server_batched.py

@@ -1858,7 +1858,6 @@ def calls_usage(self, req: tsi.CallsUsageReq) -> tsi.CallsUsageRes:
             unfinished_call_ids=sorted(unfinished_call_ids),
         )
 
-    @traced_generator(name="clickhouse_trace_server_batched.calls_query_stream")
     def _build_calls_query(
         self, req: tsi.CallsQueryReq
     ) -> tuple[CallsQuery, dict[str, Any] | None]:
@@ -1966,6 +1965,7 @@ def _build_calls_query(
 
         return cq, settings
 
+    @traced_generator(name="clickhouse_trace_server_batched.calls_query_stream")
     def calls_query_stream(self, req: tsi.CallsQueryReq) -> Iterator[tsi.CallSchema]:
         """Returns a stream of calls that match the given query."""
         cq, settings = self._build_calls_query(req)