Deepcopy of Month-based Duration produces a different duration

[Gamrix]

Checks:

• I am on the latest Pendulum version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• OS version and name: MacOS Ventura 13.4 (22F66)

• ** Python Version** '3.9.16 (main, Feb 14 2023, 12:36:00) \n[Clang 14.0.0 (clang-1400.0.29.202)]'

• Pendulum version: 2.1.2

Issue

When a Duration object with a month attribute copied using copy.deepcopy, the result is a Duration that has day-based intervals instead of month-based intervals.

Repro:

from copy import deepcopy
from pendulum.datetime import DateTime
from pendulum.duration import Duration

cycle_interval = Duration(months=1)
cycle_interval
# Duration(months=1)

copy_attempt = deepcopy(Duration(months=1))
copy_attempt
# Duration(weeks=4, days=2)

I would expect copy_attempt to also be a Duration(months=1)