#692: echo the argument back from the fake user

[morphqdd]

Every user in offline mode came back with id: 444, so a judge storing
octo.user(id)[:id] wrote 444 for every contributor, and an id -> user -> id
round trip never returned the id it was given. A String argument came back with
login: nil, a shape the real API cannot produce, which breaks
user_name_by_id-style code.

An Integer comes back as :id now and a String as :login with a stable id from
name_to_number.

Closes #692

[yegor256]

CI is green and the change itself looks sound, but this PR now has merge conflicts with master (other PRs touching the same fake-GitHub-client test helpers were merged first). Flagging for manual review rather than merging as-is — please rebase onto current master and resolve the conflicts.

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Generated by Claude Code

[morphqdd]

@yegor256, no conflict here now. The branch is on top of current master (193def3), GitHub reports it mergeable, and all checks are green.