rust-cpython: remove useless Option<$leaked> from py_shared_iterator
We no longer need to carefully drop the iterator when it's consumed. Mutation
is allowed even if the iterator exists.
There's a minor behavior change: next(iter) may return/raise something other
than StopIteration if it's called after the iterator has been fully consumed,
and if the Rust object isn't a FusedIterator.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}