Add Pyro example

[SamDuffield]

Adds example using pyro to define a model and compares against pyro and blackjax.

Also updates VI to not use torch.vmap in the case n_samples=1 since many models do not compose with torch.vmap.

[KaelanDt]

Feels a bit heavyweight for an example. What do you think of adding a simple notebook that shows the comparison between different libraries and prints out runtimes?

[SamDuffield]

Feels a bit heavyweight for an example. What do you think of adding a simple notebook that shows the comparison between different libraries and prints out runtimes?

That would be quite a long notebook, as it would need all of the bespoke code for each library.

But for sure it is heavyweight, this is due to it being replicable simulations to add to the paper rather than a pure example. I think we can solve this by adding a small extra notebook that demonstrates how to define a model in pyro and then inference with posteriors. I'll raise an issue for this