Port PR from PBS-Go: NextMillennium: Adapter and server version

[cross-repo-issue-creation]

A PR was merged over on PBS-Go

• NextMillennium: Adapter and server version prebid-server#4154
• timestamp: 2025-02-11T16:45:18Z

[Net-burst]

There is an issue in the initial porting PR: #3773
The new object should be in the request.ext whereas it was added to the request.imp[].ext. This chokes the endpoint.
@przemkaczmarek please create a new pull request with a fix.