Active integer differentiation

I think `NamedTuple`s are allowed as `Active`s, but currently, we get (may be a known problem):

```julia
julia> autodiff(x -> x.a * x.b, Active((a = 2, b = 3)))
((a = 0, b = 0),)
```

Start by reproducing the Julia REPL example with autodiff and Active on the NamedTuple. Trace how Enzyme handles Active NamedTuples and integer fields, then verify the fix by rerunning the example and confirming it produces the expected nonzero differentiation result.

Written by the indexing model from the issue text.