Breaking Change in v2.2.0: Choice Template Objects No Longer Accept Iterables.

Choice template objects used to accept probably any Iterable. I was using frozensets. But they now require tuples (maybe lists?). Not difficult to fix, but also an undocumented breaking change.

## Workaround
Submit tuples to Choice Templates.

## Resolution Suggestion

- Document the change for people migrating
- Or restore the original ability to process Iterables like frozenset for chocies.

Start by reproducing the v2.2.0 behavior with a frozenset passed to a Choice template, then compare it with the earlier iterable-accepting behavior. The issue leaves two possible outcomes: document the migration restriction and tuple workaround, or restore support for iterables such as frozenset. Done means one of those outcomes is agreed and implemented.

Written by the indexing model from the issue text.