Reduce code duplication in REST and streaming clients

The current approach for handling stocks and crypto historical data and streaming is good from the user perspective. But in fact, it's a result of a massive copy-paste-edit approach and it's hard to maintain such code in long term. I've made some changes in the 6.0.1 branch but it's not enough for a truly DRY solution.

Perspective areas of improvements:

- [ ] REST clients configuration types and related environment extension methods
- [ ] Historical data single/multi symbols requests and converting each type into another
- [x] Helper methods for ADTV calculation (how to create request type properly?)
- [x] Helper methods for SMA calculation (convert normal IEnumerable into async one)