`result.safe` for generator functions

[katunilya]

Support result safe for generator functions. Imagine we have a function that returns a generator of some typical values:

def func() -> Iterable[int]:
  yield from range(10)

Currently @result.safe_iterate decorator is useless as it won't catch an exception.

It would be better to have @result.safe_iterable decorator that would consider function to return many values and wrap each one into the Result container:

@result.safe_iterate
def func() -> Iterable[int]:  # after decorator applied signature would be () -> Iterable[Result[int, Exception]]
  yield from range(10)