Given a deeply nested array where each element is either a JSON object or another array of the same form, return a flat array containing all JSON objects in their original left-to-right order. Implement the flattening iteratively without using recursion.
Example 1:
Input: items = [{"id": 1}, [{"id": 2}, [{"id": 3}]], {"id": 4}]
Output: [{"id": 1}, {"id": 2}, {"id": 3}, {"id": 4}]
Explanation: Nested arrays are expanded while preserving object order.
Example 2:
Input: items = [[[{"name": "a"}]], [], [{"name": "b"}, [{"name": "c"}]]]
Output: [{"name": "a"}, {"name": "b"}, {"name": "c"}]
Explanation: Empty arrays contribute nothing, and all objects are collected in sequence.
0 <= len(items) <= 10^5 across all nested arrays combineddict or a list