Set up benchmarking using touchstone

[kaitejohnson]

Feature

We would like to set up performance benchmarking in CI using touchstone, consistent with the other epinowcast org packages

Preferred solution

This will require writing actual package functions and comparing to some baseline performance, as in the example here from primarycensoreddist. This will take some more thought but could be something as simple as scoring a nowcast from the package and comparing it to a naive multiplicative factor nowcast that assumes some set delay distribution.

Alternatives

We could also do this with a vignette, similar to the synthetic_validation workflow in EpiNow2 but its probably better to use CI for at least some simple functions and consider a more complicated workflow for a vignette.

[seabbs]

I would split this into sub issues for the infra and content