Skip the query cache entirely

[djmb]

We want to avoid using the ActiveRecord query cache entirely with SolidCache:

• Read queries don't need to be cached as that is handled by the local cache
• Write queries should not clear the query cache, as you would not expect Rails.cache.write to do that.

Ideally we'd just be able to do something like:

class SolidCache::Record
  self.uses_query_cache = false
end

Absent that we need to do a bunch of gymnastics to get the behaviour we want.

1. Selects - This is easy enough, we just wrap the query in an uncached block

2. Upserts - Here we need to avoid calling connection.exec_insert_all as that will dirty the query cache. Instead we have to construct the SQL manually and execute it with connection.exec_query.

3. Deletes - Similarly we need to avoid calling connection.delete here. Again we construct the SQL manually and execute it with connection.exec_delete.