Remove array caching to prevent always returning miss from memory

[rskuipers]

We were running into issues that on the first load it was giving us a miss even for subsequent calls.
What was happening was that when you retrieve something from cache that doesn't exist, it gets created but the cache item also gets saved to an array for some extra in memory caching. However, this would store the cache item with ->isHit() = false making it so that each subsequent call for retrieving that cache item would still yield a ->isHit() = false until you rerun the request where the array would be empty and it would retrieve the cache item from cache with ->isHit() = true.

This PR removes the memory caching, we should leave the caching to the CacheItemPool.
I've also added a test to cover this case.

When adding the test, another error surfaced so I fixed a type-hint as well, though I'm not fully confident that it's fully covered now, I didn't have time to dive into that area.

[jgivoni]

Thank you Rick, I will look into it.
I tend to agree that caching could be left to the CacheItemPool.
You could set up a 2-level (fast/slow) caching strategy to achieve the behavior I was going for without said bugs.

[rskuipers]

@jgivoni Thank you for the rapid response!
And indeed, I've used the Symfony Cache Chain Adapter to achieve this, so I could add an ArrayAdapter in front of my RedisAdapter.

[jgivoni]

Thank you @rskuipers for your contribution!
Merged and tagged 3.0.4