Better document the terminating behaviour of `PySeqIter_Type` in the `iter()` docs

[jonathandung]

Documentation

It is not exactly clear when the iterator returned by iter(seq) stops, where the type of seq implements __getitem__ . It was only by consulting the ABI docs that I found out it stops when IndexError is raised, and by experimenting in the console that only __length_hint__ on the iterator calls __len__ on seq if present and subtracts it by the number of items yielded. I believe this can be better documented, preferably in the iter() function documentation, which only mentions:

or it must support the sequence protocol (the __getitem__() method
with integer arguments starting at 0)

with no further explanation.

[jonathandung]

The Google Search AI output cites Stack Overflow rather than the Python docs, and Deepseek is unable to find the page I linked even when I specifically asked it to cite the Python docs.