docs: add short mode query sample & test (#1978)

* docs: add short mode query sample & test

samples/client_query_shortmode.py

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+def client_query_shortmode() -> None:
+    # [START bigquery_query_shortquery]
+    # This example demonstrates issuing a query that may be run in short query mode.
+    #
+    # To enable the short query mode preview feature, the QUERY_PREVIEW_ENABLED
+    # environmental variable should be set to `TRUE`.
+    from google.cloud import bigquery
+
+    # Construct a BigQuery client object.
+    client = bigquery.Client()
+
+    query = """
+        SELECT
+            name,
+            gender,
+            SUM(number) AS total
+        FROM
+            bigquery-public-data.usa_names.usa_1910_2013
+        GROUP BY
+            name, gender
+        ORDER BY
+            total DESC
+        LIMIT 10
+    """
+    # Run the query.  The returned `rows` iterator can return information about
+    # how the query was executed as well as the result data.
+    rows = client.query_and_wait(query)
+
+    if rows.job_id is not None:
+        print("Query was run with job state.  Job ID: {}".format(rows.job_id))
+    else:
+        print("Query was run in short mode.  Query ID: {}".format(rows.query_id))
+
+    print("The query data:")
+    for row in rows:
+        # Row values can be accessed by field name or index.
+        print("name={}, gender={}, total={}".format(row[0], row[1], row["total"]))
+    # [END bigquery_query_shortquery]

samples/tests/test_client_query_shortmode.py

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import typing
+
+from .. import client_query_shortmode
+
+if typing.TYPE_CHECKING:
+    import pytest
+
+
+def test_client_query_shortmode(capsys: "pytest.CaptureFixture[str]") -> None:
+    client_query_shortmode.client_query_shortmode()
+    out, err = capsys.readouterr()
+    assert "Query was run" in out