* first steps into async-enumerable

* move to the old iterator

* make it compile

* add missing APIs

* re-hide CursorEnumerable<T> - invent dummy enumerable APIs for now; implement KeysAsync; make pageOffset work for all; increase the default library page size, because 10 is *way* too small - noting that we still need to compare to 10 when building messages

* missing awaits

* fix range error in ValuePairInterleavedProcessorBase<T>; fix HSCAN tests

* async streams is "8.0", not "preview"

* update async enumerable API

* eek, the special compiler trick for spans only apples to byte - presumably due to endianness; this was allocating *lots*

* fix page size merge fail

* lib updates

* fix mock tests

* fix async signature detection re IAsyncEnumerable

* fix bug in interleaved pair processor

* fix more scanning glitches

* fix resume on scans

* detect and warn on thread-theft

* more logs in NoticesConnectFail