SunPhase is not thread safe

[NaanProphet]

Because of the setters on private Calendar startDate, endDate; the SunPhase class is not thread safe. And since com.florianmski.suncalc.SunCalc which calls the setters is in a different package from com.florianmski.suncalc.models.SunPhase, the setter can't even be made package private for better encapsulation.

Perhaps we SunPhase should only house the the existing constructor's final variables:

    private final Name name;
    private final double startAngle, endAngle;
    private final boolean startRise, endRise;

and then, once the date is known, we construct and return a new SunPhaseDay class once the date is specified in SunCalc#getPhases that includes:

    private final Name name;
    private final double startAngle, endAngle;
    private final boolean startRise, endRise;
    private final Calendar startDate, endDate;