Rule for `vect` unthunks many times

This:

using ChainRulesCore
myplus(x,y) = x + y
function ChainRulesCore.rrule(::typeof(myplus), x, y)
  println("myplus rrule forward")
  x+y, dz -> begin
    println("myplus rrule reverse, dz isa ", typeof(dz))
    NoTangent(), @thunk(unthunk(dz)), @thunk @show unthunk(dz)
  end
end

using Yota
grad([1,2,3]) do x
  prod(myplus(x, [4,5,6]))
end

prints this:

myplus rrule forward
myplus rrule reverse, dz isa InplaceableThunk{Thunk{ChainRules.var"#1675#1678"{Float64, Colon, Vector{Float64}, ProjectTo{AbstractArray, NamedTuple{(:element, :axes), Tuple{ProjectTo{Float64, NamedTuple{(), Tuple{}}}, Tuple{Base.OneTo{Int64}}}}}, Float64}}, ChainRules.var"#1674#1677"{Float64, Colon, Vector{Float64}, Float64}}
unthunk(dz) = [63.0, 45.0, 35.0]
unthunk(dz) = [63.0, 45.0, 35.0]  # from @show dz inside the @thunk, runs 3 times
unthunk(dz) = [63.0, 45.0, 35.0]
(315.0, (ZeroTangent(), [63.0, 45.0, 35.0]))

Almost all rules should call unthunk exactly once on their input, maybe others make the same mistake, e.g. hvcat?

Start by reproducing the ChainRulesCore and Yota example from the issue, then inspect the rules involved in the shown stack and suspected cases such as hvcat for repeated unthunk calls. Done means affected rules unthunk their inputs only once and the reproduction no longer prints repeated evaluations.