Switch VRF to use PinnedSizedBytes

Currently VRF and BatchVRF use `ForeignPtr`s for storage in their types. Switching to `PinnedSizedBYtes` will improve type safety, reduce memory overhead and will make it more consistent with the rest of crypto implementations

The issue names VRF and BatchVRF but does not identify files or tests; start by searching the repository for those type definitions and for existing crypto implementations using PinnedSizedBytes. Confirm that both types no longer use ForeignPtr storage, then run the relevant package tests and checks to verify the change.

Written by the indexing model from the issue text.