Inconsistency in shift/2 with months, years

[nallwhy]

Steps to reproduce

> start_datetime = ~U[2024-02-29 09:00:00Z]
~U[2025-02-28 09:00:00Z]

> Timex.shift(start_datetime , months: 12)
~U[2025-03-01 09:00:00Z]

> Timex.shift(start_datetime , months: 12) == Timex.shift(start_datetime , years: 1)
false

Description of issue

• What are the expected results?

The results of shifting 12 months and 1 year are the same.

[nallwhy]

In a non-leap year, a person with a birthday on 2/29 has a birthday party on 2/28.
But it's 3/1 in Timex.

timex/lib/datetime/datetime.ex

Line 566 in 22230a0

m == 2 and d == 29 and :calendar.is_leap_year(y) ->

[nallwhy]

But it's a breaking change... I can just use my own fork of Timex.