Fetch paginated data from two APIs

Write a function `get_enriched_records(api_a_url, api_b_url)`. `api_a_url` returns paginated JSON in the form: ```json { "data": [ {"id": 1, "ref_id": "x1"}, {"id": 2, "ref_id": "x2"} ], "next_page": 2 } ``` `api_b_url` returns paginated JSON in the form: ```json { "data": [ {"ref_id": "x1", "target_field": "value1"}, {"ref_id": "x2", "target_field": "value2"} ], "next_page": null } ``` Implement the function so that it: 1. Retrieves **all pages** from both APIs. 2. Joins the records from the two endpoints using `ref_id`. 3. Returns a list of objects in the form `{ "id": <id>, "target_field": <value> }`. 4. Preserves the order of records from `api_a_url`. 5. Skips any record if: - `ref_id` is missing, - the matching record does not exist in the second API, - `target_field` is `null`, an empty string, or whitespace-only. 6. Handles missing keys, empty pages, and `None` values safely without crashing. 7. Uses normal HTTP request handling; assume the test harness will mock the API responses. The focus is not on advanced algorithms, but on clean API retrieval logic, pagination handling, and defensive data validation.