`serai_core_pallet` solely defines an accumulator for the events. We use the
traditional `frame_system::Events` to store them for now and enable retrieval.
Adds a deny entry for `is-terminal` to stop it from secretly reappearing.
Restores the `is-terminal` patch for `is_terminal_polyfill` to have one less
external dependency.
Actually use the added `Allocations` abstraction
Start using the sessions API in the validator-sets pallet
Get a `substrate/validator-sets` approximate to compiling
