📝🐞 ieee1788-elem.jl - sheNaNigans and atan2

[miguelraz]

From the test suite

@test nai() + DecoratedInterval(Interval(1.0, 2.0), trv) == nai()
@test nai() - DecoratedInterval(Interval(1.0, 2.0), trv) == nai()
@test nai() * DecoratedInterval(Interval(1.0, 2.0), trv) == nai()
@test nai() / DecoratedInterval(Interval(1.0, 2.0), trv) == nai()
@test  +(nai()) == nai()
@test -(nai()) == nai()

As well as

• the entire atan2 functionality. (this should be fixed here)

[miguelraz]

Tests pass on the test suite with atan2 -> atan. 👍

[lucaferranti]

superseeded by #465