Keep underlying exception traceback on Err.unwrap if available

[katunilya]

When we invoke Err.unwrap we can accidentally lose information about underlying error. If Err internal value is of type Exception / BaseException (somewhere in inheritance hiearachy) then when we raise ErrUnwrapError we should also include underlying exception.

How it works now?

def div(a, b) -> Result[float, Exception]:
  try:
    return Ok(a / b)
  except Exception as exc:
    return Err(exc)

div(1, 0).unwrap()  # raises ErrUnwrapError, but looses ZeroDivisionError

How it should work?

def div(a, b) -> Result[float, Exception]:
  try:
    return Ok(a / b)
  except Exception as exc:
    return Err(exc)

div(1, 0).unwrap()  # raises ErrUnwrapError, but also includes information about ZeroDivisionError in traceback