refactor: clean up 3-tuple cross product into more readable form

stdlib/LinearAlgebra/src/generic.jl

@@ -386,11 +386,11 @@ function cross(a::AbstractVector, b::AbstractVector)
     if !(length(a) == length(b) == 3)
         throw(DimensionMismatch("cross product is only defined for vectors of length 3"))
     end
-    collect(cross((a[1], a[2], a[3]), (b[1], b[2], b[3])))
-end
-function cross(a::Tuple{Vararg{Any, 3}}, b::Tuple{Vararg{Any, 3}})
     a1, a2, a3 = a
     b1, b2, b3 = b
+    collect(cross((a1, a2, a3), (b1, b2, b3)))
+end
+function cross((a1, a2, a3)::Tuple{Vararg{Any, 3}}, (b1, b2, b3)::Tuple{Vararg{Any, 3}})
     (a2*b3-a3*b2, a3*b1-a1*b3, a1*b2-a2*b1)
 end