Optimize reading a single value from the result set

When the query is a `First` or `FirstOrDefault`, then we know that we will only ever read zero or one row from the reader. We might be able to make this more efficient. For example, [CommandBehavior.SingleRow](https://learn.microsoft.com/en-us/dotnet/api/system.data.commandbehavior?view=net-7.0) may help on some providers. In addition, we may be able to make the query execution delegate that we generate more efficient.