feat: implement windowOrganicResults function and update DuckDuckGo search logic

[subediparas5]

Summary

• Keep a single DuckDuckGo browser page open and click “More Results” until enough organic results are loaded.
• Deduplicate refreshed results and apply start and limit without counting ads.
• Preserve SERP feature extraction from the initial result page.

Why

• Fixes bug: DuckDuckGo search returning incorrect results for non-zero offsets #40.
• DuckDuckGo dynamically loads additional results, so generated pagination URLs returned incomplete, duplicated, or incorrect results for non-zero offsets.

Testing

• make test
• make lint
• make test-integration (only for browser, proxy, captcha, or live-engine changes)

Checklist

• I linked the related issue or explained why there is none.
• I updated docs or examples for changed user-facing behavior.
• I kept unit tests deterministic and free of browser/network dependencies.
• I removed secrets, proxy credentials, and private logs from examples.

[karust]

Nice fix, I reviewed and reproduced the problem .

I pushed one small commit on top: added fallback selector and test for "more results" button + updated HTML page used in tests.

Thanks for the contribution!