Support tuples as keys for get_all/put_all callbacks in Redis/Client cluster

[DanielKulesza]

In the Nebulex README Quickstart example, there are cases where the keys are Elixir tuples.

  @decorate cache_evict(
              cache: Cache,
              keys: [{User, user.id}, {User, user.username}]
            )
  def delete_user(%User{} = user) do
    Repo.delete(user)
  end

Tuples as keys work perfectly fine in nebulex_redis_adapter with a standalone Redis instance. They also work fine with nebulex_redis_adapter in redis_cluster/client_cluster mode for get/put callbacks.

However, get_all and put_all callbacks don't work properly with tuples as keys.
When running those callbacks with tuples as keys, CROSSLOT errors often occur.

Example:

 1) test MOVED put and get operations with tuple keys (NebulexRedisAdapter.RedisClusterTest)
     test/nebulex_redis_adapter/redis_cluster_test.exs:188
     ** (Redix.Error) CROSSSLOT Keys in request don't hash to the same slot
     code: assert Cache.get_all([{RedisCache.Testing, "key1"}, {RedisCache.Testing, "key2"}]) == %{
     stacktrace:
       (nebulex_redis_adapter 2.3.1) lib/nebulex_redis_adapter/command.ex:167: NebulexRedisAdapter.Command.handle_command_response/2
       (nebulex_redis_adapter 2.3.1) lib/nebulex_redis_adapter.ex:559: NebulexRedisAdapter.mget/4
       (nebulex_redis_adapter 2.3.1) lib/nebulex_redis_adapter.ex:542: anonymous fn/4 in NebulexRedisAdapter.do_get_all/3
       (stdlib 3.17.2.1) maps.erl:410: :maps.fold_1/3
       (nebulex_redis_adapter 2.3.1) lib/nebulex_redis_adapter.ex:530: anonymous fn/4 in NebulexRedisAdapter.get_all/3
       (telemetry 1.2.1) /Users/Daniel.Kulesza/Projects/nebulex_redis_adapter/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
       test/nebulex_redis_adapter/redis_cluster_test.exs:194: (test)

This appears because the group_keys_by_hash_slot function takes an Enum.t() of:

• any values as keys when grouping keys for a get_all
  OR
• tuples of key-value pairs when grouping keys for a put_all

The change in this Pull Request aims to resolve this issue by specifying an atom (:keys/:tuples) as an argument to differentiate between the two cases.

[cabol]

Nice! Thanks for the fix!