Fixing bug related to http fetcher accumulating query params from multiple calls

[karwaankit32]

Fix: Prevent duplicate account IDs in query parameters when fetching accounts

Problem

When FetchAccounts is called multiple times, the same account ID appears multiple times in the query string. For example, instead of ?account-id=280, the query becomes ?account-id=280&account-id=280.

Root Cause

In the FetchAccounts method, the code creates a reference to fetcher.EndpointURL rather than a copy:

u := fetcher.EndpointURL
q := u.Query()

Fixing that by creating a deep copy.

Testing

Tested by locally running prebid-server and hitting cookie_sync endpoint multiple times in succession to find endpoint being hit correctly.