@select(
    comptime T: type,
    pred: std.meta.Vector(len, bool),
    a: std.meta.Vector(len, T),
    b: std.meta.Vector(len, T)
) std.meta.Vector(len, T)

Constructs a vector from a & b, based on the values in the predicate vector. For indices where the predicate value is true, the corresponding
element from the a vector is selected, and otherwise from b.