test(admin): fix stale-claim networking test flake

[eventualbuddha]

Overview

The waitFor for the client's disconnect could sometimes advance fake time past STALE_MACHINE_THRESHOLD_MS on a loaded machine. This made it release the claim before the test asserted it survived a short disconnect. Do the assert after a shorter fixed time advance instead.

Demo Video or Screenshot

From the failing job:

 FAIL  src/app_networking.test.ts > a ballot claimed via the peer API is released when the client goes stale
AssertionError: expected 'e636583f-0b7a-4a5b-bee1-be8e49dff226' to be undefined

- Expected:
undefined

+ Received:
"e636583f-0b7a-4a5b-bee1-be8e49dff226"

 ❯ src/app_networking.test.ts:465:63
    463|
    464|   // The claim survives a disconnect shorter than the stale threshold
    465|   expect(claimNextOnHost(store, electionId, 'OTHER-MACHINE')).toBeUnde…
       |                                                               ^
    466|
    467|   // Once the client is stale, the host's polling loop releases the cl…

Testing Plan

Ran locally with an artificially-inflated fake time advance and saw it reproduce consistently.