Batch seal verification implementation

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Parallelized seal verification using Rayon
  • Can't do with a hashmap input (to match go interface 1:1) but looking at the usage it seems better to do as a vector anyway, which can just be referenced to pass into this.
  • Not really much option to have a more generic interface, because it depends on the IntoParallelRefIterator trait, and that forces a specific implementation (which will then be incompatible with MockRuntime needs)

Seems like the best solution than managing threads in an async context, but very open to suggestions on how this can be parallelized better

Reference issue to close (if applicable)

Closes #457

Other information and links