BUG: date_range ignores nanoseconds component of DateOffset frequency

[shwina]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the master branch of pandas.

Reproducible Example

import pandas as pd

pd.date_range(start='2001-01-01', freq=pd.DateOffset(nanoseconds=1), periods=3).to_numpy()

Issue Description

Greetings!

When specifying the frequency as a DateOffset object, Pandas seems to ignore the frequency entirely if it consists solely of a nanoseconds component:

In [6]: pd.date_range(start='2001-01-01', freq='1ns', periods=3).to_numpy()
Out[6]:
array(['2001-01-01T00:00:00.000000000', '2001-01-01T00:00:00.000000001',
       '2001-01-01T00:00:00.000000002'], dtype='datetime64[ns]')

In [7]: pd.date_range(start='2001-01-01', freq=pd.DateOffset(nanoseconds=1), periods=3).to_numpy()
Out[7]:
array(['2001-01-01T00:00:00.000000000', '2001-01-02T00:00:00.000000000',
       '2001-01-03T00:00:00.000000000'], dtype='datetime64[ns]')

or, if it consists of multiple components, ignores the nanoseconds part:

In [8]: pd.date_range(start='2001-01-01', freq=pd.DateOffset(days=1, nanoseconds=1), periods=3).to_numpy()
Out[8]:
array(['2001-01-01T00:00:00.000000000', '2001-01-02T00:00:00.000000000',
       '2001-01-03T00:00:00.000000000'], dtype='datetime64[ns]')

Expected Behavior

import pandas as pd
import numpy as np

expect = pd.date_range(start='2001-01-01', freq='1ns', periods=3).to_numpy().astype('int64')
got = pd.date_range(start='2001-01-01', freq=pd.DateOffset(nanoseconds=1), periods=3).to_numpy().astype('int64')
np.testing.assert_equal(expect, got)

Installed Versions

Replace this line with the output of pd.show_versions()

[mroeschke]

Thanks for the report. I believe the core issue was reported in #43892 so closing to close this in favor of that.