xr.cftime_range fails when using proleptic_gregorian calendar in cftime.datetime object

What happened?

I want to use the xarray.cftime_range function to get a set of datetimes between two cftime.datetime objects that use the proleptic_gregorian calendar. However, when I use this function with this calendar, I receive the following error:

File "/Users/Alexander/miniconda3/envs/xrtest/lib/python3.11/site-packages/xarray/core/resample_cftime.py", line 491, in exact_cftime_datetime_difference
    seconds = b.replace(microsecond=0) - a.replace(microsecond=0)
              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
  File "src/cftime/_cftime.pyx", line 1574, in cftime._cftime.datetime.__sub__
TypeError: cannot compute the time difference between dates with different calendars

What did you expect to happen?

I expect this function to return a list of dates between the two dates I selected, with each date spaced by one day. In the minimal example, I provide the expected output obtained when I instead use the cftime.DatetimeProlepticGregorian object.

Minimal Complete Verifiable Example

#xarray==2024.3.0
#cftime==1.6.3
import xarray as xr
import cftime

start_date = cftime.DatetimeProlepticGregorian(1,1,1)
end_date = cftime.DatetimeProlepticGregorian(2,1,1)

daterange = xr.cftime_range(start_date, end_date, calendar='proleptic_gregorian')
print(daterange)

start_date = cftime.datetime(1,1,1,calendar = 'proleptic_gregorian')
end_date = cftime.datetime(2,1,1,calendar = 'proleptic_gregorian')

daterange = xr.cftime_range(start_date, end_date, calendar='proleptic_gregorian')
print(daterange)

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

No response

Anything else we need to know?

No response

Environment

Start in xarray/core/resample_cftime.py at exact_cftime_datetime_difference and reproduce the cftime_range example with both kinds of proleptic_gregorian cftime.datetime objects. Trace why the subtraction reports different calendars, then verify that xr.cftime_range returns dates spaced one day apart for the provided inputs.