replace the RAYON_INITIALIZE `LazyLock` with a local `Once`
Since we don't actually need this `LazyLock` to contain data, I think
using a `Once` is slightly more idiomatic. `LazyLock` contains a `Once`
internally, so the actual synchronization that's happening in practice
is the same either way. (I noticed this while looking at how we use
`LazyLock` across our repos.)
