Support for tracked SharedArrays?

Currently, a SharedArray becomes non-shared when passed to the function param.

```julia
julia> W = SharedArray(rand(4, 3))
b = SharedArray(rand(4))
l = Dense(param(W), param(b), relu)
l.W.data
4×3 Array{Float64,2}:
0.97669 0.26793 0.893204
0.775216 0.679546 0.176578
0.857517 0.289327 0.0719966
0.638023 0.0768014 0.669786
```
Would it be easily possible to keep it shared?

Reproduce the Julia example using SharedArray, param, Dense, and relu, then trace where the parameter is converted before it appears as l.W.data. Determine how shared storage should be preserved while tracking remains correct. Done means SharedArray inputs remain shared in the resulting tracked parameters without breaking existing behavior.

Written by the indexing model from the issue text.