Switch to `SimpleVarInfo` for better computational efficiency

[yebai]

SimpleVarInfo in DynamicPPL provides significant speedup over the current implementation. We should consider switching to use it once TuringLang/DynamicPPL.jl#360 is merged.

[storopoli]

Does that change how we would write the model inside the @model block?

[yebai]

It should just work once the SimpleVarInfo integration with Turing is complete. But it is perhaps a good idea to test it on GLM models when it becomes available.

[storopoli]

@yebai has this been already merged into Turing.jl?

[yebai]

We are very close now - only one final PR standing. Hopefully, it will get reviewed and merged this week or next.

[storopoli]

Ok I subscribed to it and once it is merged and a new Turing version is tagged I will run tests.