fix(bigquery): address review comments on memory-limited fetch

- Use has_app_context()/has_request_context() guards so fetch_data
  is safe to call outside a Flask request (fixes RuntimeError on g
  writes and current_app access in non-request paths)
- Replace sys.getsizeof(str(batch)) with per-row getsizeof sum for
  more accurate memory estimation without the str() allocation
- Fix false-positive truncation: fetch remaining+1 rows and check
  len > remaining to confirm more data exists beyond the cap
- Reset g.bq_memory_limited/g.bq_memory_limited_row_count after
  reading in get_df_payload to prevent flag leaking across multiple
  queries in the same request
- Wrap warning string in _() for i18n
- Add warning field to ChartDataResponseResult Marshmallow schema
- Pass noDuplicate: true to addWarningToast to suppress duplicate
  toasts when a multi-query chart has multiple truncated responses

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

superset/common/query_context_processor.py

@@ -193,11 +193,17 @@ class QueryContextProcessor:
         warning: str | None = None
         if getattr(g, "bq_memory_limited", False):
             row_count = getattr(g, "bq_memory_limited_row_count", len(cache.df))
+            # Reset flags immediately so subsequent queries in the same request
+            # don't inherit this warning
+            g.bq_memory_limited = False
+            g.bq_memory_limited_row_count = 0
             chart_id = (self._query_context.form_data or {}).get("slice_id", "")
             prefix = f"Chart {chart_id}: " if chart_id else ""
-            warning = (
-                f"{prefix}Results truncated to {row_count:,} rows"
-                " due to memory constraints."
+            warning = _(
+                "%(prefix)sResults truncated to %(row_count)s rows"
+                " due to memory constraints.",
+                prefix=prefix,
+                row_count=f"{row_count:,}",
             )
 
         return {