Get/Select SHOULD NOT release queries

[jgiles]

Currently, the Get and Select iterx methods call iter.ReleaseQuery(). This is a highly dangerous "convenience" which can lead to data races under common usage patterns.

The Iter constructor and Get and Select functions accept a query as a parameter, and so from an API design perspective it make most sense to let clients (who created the query) manage the query lifecycle.

E.g. it's a pretty common pattern to do

q := createQuery()
defer q.Release()
// do stuff with query, err returns, etc
return result, nil

But if "doing stuff" includes a gocqlx.Select, this pattern will lead to Release being called twice. That means the query object now has two entries in the query pool, which will distribute it to two separate goroutines, and racy concurrent read/writes ensue. We had a very hard-to-track-down bug in our service caused by this.

In this case, the cost of not calling Release is minimal; the query will just be GC'd instead of recycled. It's safer and better to let clients do releasing themselves.