* checked exceptions in stores
* makes asynciter as much exception safe as it gets
* introduce "SafeAsyncIter" that uses Results and limits exceptions to cancellations
* adds {.push raises: [].} to errors
* uses SafeAsyncIter in "listBlocks" and in "getBlockExpirations"
* simplifies safeasynciter (magic of auto)
* gets rid of ugly casts
* tiny fix in hte way we create raising futures in tests of safeasynciter
* Removes two more casts caused by using checked exceptions
* adds an extended explanation of one more complex SafeAsyncIter test
* adds missing "finishOnErr" param in slice constructor of SafeAsyncIter
* better fix for "Error: Exception can raise an unlisted exception: Exception" error.
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Co-authored-by: Dmitriy Ryajov <dryajov@gmail.com>
* Rework AsyncIter
* Add tests for finishing iter on error
* Improved error handling for and additional tests
* Use new style of constructors
* Handle future cancellation
* Docs for constructors
