message: add test for date_format option
diff: @@ -3,6 +3,7 @@ import tempfile
  import os
  import pandas as pd
  import tempfile
  +import pandas._testing as tm
  class TestToCSV(object):
  def test_basic_to_csv(self):
  @@ -69,3 +70,18 @@ class TestToCSV(object):
  rel.to_csv(temp_file_name, header=True, quotechar='"', escapechar='!')
  csv_rel = duckdb.read_csv(temp_file_name, quotechar='"', escapechar='!')
  assert rel.execute().fetchall() == csv_rel.execute().fetchall()
  +
  + def test_to_csv_datetime(self):
  + temp_file_name = os.path.join(tempfile.mkdtemp(), next(tempfile._get_candidate_names()))
  + df = pd.DataFrame(tm.getTimeSeriesData())
  + dt_index = df.index
  + df = pd.DataFrame(
  + {"A": dt_index, "B": dt_index.shift(1)}, index=dt_index
  + )
  + rel = duckdb.from_df(df)
  + rel.to_csv(temp_file_name, date_format="%Y%m%d")
  +
  + csv_rel = duckdb.read_csv(temp_file_name, date_format="%Y%m%d")
  + print(csv_rel)
  +
  + assert rel.execute().fetchall() == csv_rel.execute().fetchall()
  