feat(bigquery): add PendingDeprecationWarning for from_dataframe methods

[shuoweil]

Adds PendingDeprecationWarning to Client.load_table_from_dataframe() and Client.insert_rows_from_dataframe() in google-cloud-bigquery.

This alerts users to adopt direct pandas_gbq.to_gbq() entry points ahead of future deprecation phases per the pandas-gbq migration design.

• Added PendingDeprecationWarning to load_table_from_dataframe and insert_rows_from_dataframe in google/cloud/bigquery/client.py.
• Added corresponding unit tests in tests/unit/test_client.py.

Fixes #<526614511 🦕

[gemini-code-assist]

Code Review

This pull request deprecates loading and inserting rows from DataFrames via google-cloud-bigquery by introducing PendingDeprecationWarning warnings and adding corresponding unit tests. Feedback on the changes highlights two issues: first, assertions for an existing test (test_insert_rows_from_dataframe_w_explicit_none_insert_ids) were accidentally deleted and need to be restored; second, the use of parenthesized context managers in the tests breaks compatibility with Python 3.8 and should be replaced with standard multi-context with statements.

[gemini-code-assist]

The assertions for test_insert_rows_from_dataframe_w_explicit_none_insert_ids were accidentally deleted when adding the new test test_insert_rows_from_dataframe_emits_pending_deprecation_warning. Please restore the deleted assertions and append the new test case.

        EXPECTED_SENT_DATA = {
            "rows": [
                {"insertId": None, "json": {"name": "Little One", "adult": "false"}},
                {"insertId": None, "json": {"name": "Young Gun", "adult": "true"}},
            ]
        }

        actual_calls = conn.api_request.call_args_list
        assert len(actual_calls) == 1
        assert actual_calls[0] == mock.call(
            method="POST",
            path=API_PATH,
            data=EXPECTED_SENT_DATA,
            timeout=DEFAULT_TIMEOUT,
        )

    def test_insert_rows_from_dataframe_emits_pending_deprecation_warning(self):
        pandas = pytest.importorskip("pandas")
        from google.cloud.bigquery.schema import SchemaField
        from google.cloud.bigquery.table import Table

        creds = _make_credentials()
        http = object()
        client = self._make_one(project=self.PROJECT, credentials=creds, _http=http)
        client._connection = make_connection({}, {})

        schema = [SchemaField("name", "STRING", mode="REQUIRED")]
        table = Table(self.TABLE_REF, schema=schema)
        dataframe = pandas.DataFrame([{"name": "Alice"}])

        with pytest.warns(
            PendingDeprecationWarning,
            match="Inserting rows from DataFrames via google-cloud-bigquery is deprecated",
        ):
            client.insert_rows_from_dataframe(table, dataframe)

[shuoweil]

fixed

[gemini-code-assist]

Parenthesized context managers are only supported in Python 3.9+. To maintain compatibility with Python 3.8 (which is still supported by this package), use a standard multi-context with statement without parentheses.

        with load_patch, get_table_patch, pytest.warns(
            PendingDeprecationWarning,
            match="Loading DataFrames via google-cloud-bigquery is deprecated",
        ):

[shuoweil]

fixed