Clearer Error when KeyError

[bashirmindee]

Currently when accessing an index/key that doesn't exist in a given object or if an object is not indexable, the error message is not clear enough. it should mention which object it is referring too. reproduce issue

from tawazi import xn, dag
@xn
def none(): return None
@dag
def pipe(): none()['a']

[bashirmindee]

The error should be clear enough even with multiple indices