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fix(deque): capture buf, head and len together in iterators (#4742)

`iter`, `iter2`, `rev_iter` and `rev_iter2` captured `len` when created
but read the live `buf` and `head` on every step. If the deque was
modified in between, the iterator combined an old length with a new
buffer or head:

- After `pop_front`, it read slots past the live range that were never
  written: phantom values on wasm and wasm-gc, a TypeError on js, and
  an abort on native.
- After `clear()` + `shrink_to_fit()`, the buffer has length 0, so
  `% buf.length()` divided by zero.

Capture `(buf, head, len)` together, as `Array::iter` does through its
view. `Queue::iter` goes through `Deque::iter`, so it is fixed too.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

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