Function observational_islamic_from_fixed 

pub fn observational_islamic_from_fixed(
    date: RataDie,
    location: Location,
) -> (i32, u8, u8)

Calculates an Islamic date from a RataDie and Location.

This uses the phasis criterion proposed by S. K. Shaukat¹, explained in Reingold section 14.9.

Lisp code reference: https://github.com/EdReingold/calendar-code2/blob/1ee51ecfaae6f856b0d7de3e36e9042100b4f424/calendar.l#L6983-L6995

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1. K. Abdali, O. Afzal, I. A. Ahmad, M. Durrani, A. Salama, and S. K. Shaukat, “Crescent Moon Visibility: Consensus on Moon-Sighting and Determination of an Islamic Calendar,” manuscript, 1996. ↩