Add explicit copy(x::TrackedArray) method

src/tracker/array.jl

@@ -43,6 +43,8 @@ end
 
 Base.print_array(io::IO, x::TrackedArray) = Base.print_array(io, data(x))
 
+Base.copy(x::TrackedArray) = copy(data(x))
+
 Base.setindex!(xs::TrackedArray, v, i...) =
   error("Can't differentiate `setindex!`")
 

src/tracker/scalar.jl

@@ -23,6 +23,8 @@ end
 
 Base.decompose(x::TrackedReal) = Base.decompose(data(x))
 
+Base.copy(x::TrackedArray) = copy(data(x))
+
 Base.convert(::Type{T}, x::TrackedReal{S}) where {T<:Real,S} = convert(T, data(x))
 
 Base.convert(::Type{TrackedReal{T}}, x::TrackedReal{T}) where T = x