Deduplicate URLs before fetching and validate behavior

Extend the sequential URL fetcher by deduplicating URLs before sending requests. Requirements Input: a list of URLs that may contain duplicates. Behavior: fetch only unique URLs (optionally preserving first-seen order). Output: results for the deduplicated URLs (same result shape as before). Describe/implement a test approach that proves deduplication happened (e.g., assert number of actual HTTP hits against a mock server). Constraints 1 ≤ n ≤ 200 Example Input: [A, B, A, C, B] Output: fetch only A, B, C once each and return 3 results. Example Input (mock) ["/a","/b","/a","/c"] Output 3 results for /a,/b,/c and mock hit counts: a=1,b=1,c=1