Fix RNG reproducibility wrapper around non-RNG quantity

[brookslogan]

In the "get started" vignette, there is the following bit of code:

withr::with_rng_version("3.0.0", withr::with_seed(42, length(state)))

This presumably should have been one of the following:

• something like runif(length(state))
• just some arbitrary number or sequence without the with_rng_version and with_seed