[BUG] Incorrect origin periods in non-standard Quarterly Triangles

Describe the bug The origin periods are incorrect when creating a quarterly triangle object with non-standard Quarter periods (Feb-Apr, May-Jul, Aug-Oct, Nov-Jan). IN my example below, I have non-standard quarter periods and when I try to create a Triangle object from the data, I get incorrect origin periods. The amounts seem to lagging. Compare the below image with the pandas dataframe.

To Reproduce Steps to reproduce the behavior. Code should be self-contained and runnable against publicly available data. For example:

import chainladder as cl
import pandas as pd
data= pd.DataFrame([
    ["5/1/2023", 12, '4/30/2024', 100],
    ["8/1/2023", 9, "4/30/2024", 130],
    ["11/1/2023", 6, "4/30/2024", 160],
    ["2/1/2024", 3, "4/30/2024", 140]], 
    columns = ['origin', 'development', 'valuation', 'EarnedPremium'])
triangle = cl.Triangle(
data, origin='origin', origin_format='%Y-%m-%d', development='valuation', columns='EarnedPremium', trailing=True, cumulative=True
)
data_from_tri = triangle.to_frame(origin_as_datetime=True)

Expected behavior: The periods seem to not match with the original data. The expected result should look something like this:

Desktop (please complete the following information):

Numpy Version 1.26.4
Pandas Version 2.2.2
Chainladder Version 0.8.20

casact / chainladder-python

[BUG] Incorrect origin periods in non-standard Quarterly Triangles #529