itertools.chain should evaluate lazily

CPython:
```
>>> from itertools import *
>>> a = chain.from_iterable(repeat(range(2)))
>>> next(a)
0
>>> next(a)
1
>>> next(a)
0
```

RustPython does not evaluate lazily and the call to `from_iterable` never returns:
```
>>>>> from itertools import *
>>>>> a = chain.from_iterable(repeat(range(2)))
```