Monitor whether ConfigureAwait(false) still problematic in specs

In https://github.com/corvus-dotnet/Corvus.Extensions/pull/53#pullrequestreview-344062016 @mwadams asked me to remove all `ConfigureAwait(false)` calls in specs. However, on further discussion, we now suspect this is no longer required. So we're going to try without it, and see how it goes. This work item is to keep track of the fact that we're monitoring this.

Start by reviewing the PR #53 review discussion linked in the issue, then inspect the specs for ConfigureAwait(false) calls. Run the relevant specs with and without those calls; done requires a clear decision about whether they remain problematic and a documented outcome.

Written by the indexing model from the issue text.