fix(test): fully resolve spub/ssub auto-resubscription race condition

[rit3sh-x]

Summary

• Follow-up to fix(test): race condition in spub/ssub auto-resubscription test #2092
• Await initial ssubscribe calls so channels are registered before disconnect
• Poll for stub.callCount >= 3 instead of relying on ping() as a barrier

Test plan

• All 555 tests passing, 0 failures
• Stable under nyc coverage overhead

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Note

Low Risk
Low risk: test-only changes that make the auto-resubscribe assertions deterministic by removing timing races around ssubscribe and reconnect.

Overview
Makes the spub/ssub auto-resubscription functional test deterministic by awaiting initial ssubscribe calls before disconnecting and by polling the ssubscribe stub until all expected resubscribe calls have occurred (instead of assuming ping() is a sufficient barrier).

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[PavelPashov]

@rit3sh-x thanks, I'll take a look