Int64 Poisson distribution sampling

The [Poisson distribution](https://dotnet.github.io/infer/apiguide/api/Microsoft.ML.Probabilistic.Distributions.Poisson.html#Microsoft_ML_Probabilistic_Distributions_Poisson_Sample) implements [IDistribution](https://dotnet.github.io/infer/apiguide/api/Microsoft.ML.Probabilistic.Distributions.IDistribution-1.html)<[Int32](https://docs.microsoft.com/dotnet/api/system.int32)> and offers
[Sample](https://dotnet.github.io/infer/apiguide/api/Microsoft.ML.Probabilistic.Distributions.Poisson.html#Microsoft_ML_Probabilistic_Distributions_Poisson_Sample) for distribution sampling in the `int32` range. For various use cases, we need an `int64/long` instead. Could this be added? 🙏