The local store implementation is causing a double serialization

[casperisfine]

When fetching a value from Memcached we deserialize it with the actual coder, but then it is put into the local cache and there it's serialized again but with Marshal to make a copy

This is wasteful, we should be able to store the payload we got from Memcached directly.

Ref: rails/rails#48302

cc @felix-d @Shopify/rails

[etiennebarrie]

Related: https://github.com/Shopify/shopify/pull/307879