Represent tombstones for deleted objects. Saves only URI
@type t() :: %Mobilizon.Tombstone{ __meta__: term(), actor: Mobilizon.Actors.Actor.t(), actor_id: term(), id: term(), inserted_at: term(), updated_at: term(), uri: String.t() }
@spec create_tombstone(map()) :: {:ok, t()} | {:error, Ecto.Changeset.t()}
@spec delete_actor_tombstones(String.t() | integer()) :: {integer(), nil}
@spec delete_uri_tombstone(String.t()) :: {integer(), nil}
@spec find_tombstone(String.t()) :: t() | nil