Other days in `days_of_month` are ignored when -1 is in the array

[marcojulian]

When creating a monthly recurrence rule, if I add a -1 to days_of_month all the other days in the array are ignored.

iex(5)> schedule = Cocktail.schedule(~N[2025-02-01 00:00:00])
#Cocktail.Schedule<>
iex(6)> schedule = Cocktail.Schedule.add_recurrence_rule(schedule, :monthly, days_of_month: [1, 10, 20, -1])
#Cocktail.Schedule<Monthly>
iex(7)> Cocktail.Schedule.occurrences(schedule) |> Enum.take(5)
[~N[2025-02-28 00:00:00], ~N[2025-03-31 00:00:00], ~N[2025-04-30 00:00:00],
 ~N[2025-05-31 00:00:00], ~N[2025-06-30 00:00:00]]

iex(8)> schedule = Cocktail.schedule(~N[2025-02-01 00:00:00])
#Cocktail.Schedule<>
iex(9)> schedule = Cocktail.Schedule.add_recurrence_rule(schedule, :monthly, days_of_month: [-1, 1, 10, 20])
#Cocktail.Schedule<Monthly>
iex(10)> Cocktail.Schedule.occurrences(schedule) |> Enum.take(5)
[~N[2025-02-28 00:00:00], ~N[2025-03-31 00:00:00], ~N[2025-04-30 00:00:00],
 ~N[2025-05-31 00:00:00], ~N[2025-06-30 00:00:00]]

Expected result:

iex(5)> schedule = Cocktail.schedule(~N[2025-02-01 00:00:00])
#Cocktail.Schedule<>
iex(6)> schedule = Cocktail.Schedule.add_recurrence_rule(schedule, :monthly, days_of_month: [1, 10, 20, -1])
#Cocktail.Schedule<Monthly>
iex(7)> Cocktail.Schedule.occurrences(schedule) |> Enum.take(5)
[~N[2025-02-01 00:00:00], ~N[2025-02-10 00:00:00], ~N[2025-02-20 00:00:00],
 ~N[2025-02-28 00:00:00], ~N[2025-03-01 00:00:00]]