app: fix flaky TestStartChecker

[KaloyanTanev]

Stop advancing the fake clock inside the success-path Eventually of TestStartChecker. The clock advances were unsynchronized with the ready-checker goroutine, so under CI load it could observe two epoch rollovers with only the single recorded vapi call, permanently flipping readiness to errReadyVCNotConnected and failing the test. The ticks fired by the two initial advances are sufficient, and the ready state is then stable, so the test now just polls for it.

category: test
ticket: none

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.36%. Comparing base (8070ac6) to head (7f7c29a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4654      +/-   ##
==========================================
- Coverage   58.36%   58.36%   -0.01%     
==========================================
  Files         247      247              
  Lines       34094    34094              
==========================================
- Hits        19900    19899       -1     
- Misses      11718    11719       +1     
  Partials     2476     2476              

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