Read full stream to ensure CannotCache statements do not leak if stream is dropped prematurely

[lukezbihlyj]

Fixes #269, gives the expected output in the same test case:

Using .load().await?.get(0)
Executing MaybeCached::CannotCache statement: 323
Yielder for statement: 323
Yielder for statement: 323, finished polling result stream
Closing MaybeCached::CannotCache statement: 323
Using .get_result().await.optional()?
Executing MaybeCached::CannotCache statement: 324
Yielder for statement: 324
Yielder for statement: 324, finished polling result stream
Closing MaybeCached::CannotCache statement: 324

[weiznich]

Thanks for opening this PR. I mostly leave this comment here to indicate that I'm aware of this issue and your contribution, but that I did not have the time yet to look into this in detail.

Is there any chance that you can address the CI errors?

[lukezbihlyj]

I'm going to investigate the lifetime issues in some of the tests and see if I can find an easy fix