test: poll for dataset items in crawlee e2e tests

[vdusek]

test_playwright_crawler failed on master (run 31375518173) with AssertionError: Missing product: Widget A / assert 'Widget A' in {}, while the run itself succeeded and assert items.count == 3 passed on the line above.

The dataset read in verify_crawler_results happens immediately after the run finishes. The API returned an empty item list while its pagination headers already reported the final item count, and DatasetItemsPage.count is max(x-apify-pagination-count, len(items)) - so the count assertion passed on the headers alone and the test only broke once it looked at the items.

The read now polls with poll_until_condition (30s ceiling) until all pushed items are returned, and asserts on len(items.items) instead of the header-derived count, which was the misleading part. The helper is shared by all six crawler e2e tests.

Verified by replaying the exact response shape from CI (empty items, count=3): the old helper reproduces Missing product: Widget A, the new one passes after polling, an immediately consistent read still takes a single call, and wrong or extra items still fail fast. tests/e2e/test_crawlee against the platform: test_playwright_crawler, test_adaptive_playwright_crawler, test_http_crawler and test_basic_crawler pass; test_parsel_crawler and test_beautifulsoup_crawler could not run on my account (Actor-count limit), they fail before reaching this helper.

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.18%. Comparing base (3212e1c) to head (b758064).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1086      +/-   ##
==========================================
- Coverage   92.24%   92.18%   -0.07%     
==========================================
  Files          51       51              
  Lines        3249     3249              
==========================================
- Hits         2997     2995       -2     
- Misses        252      254       +2     

Flag	Coverage Δ
e2e	35.24% <ø> (ø)
integration	56.66% <ø> (ø)
unit	84.45% <ø> (-0.07%)	⬇️

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