Unit tests that use `NetworkInterfaceMock` can hang indefinitely when an alarm is canceled.
In CI this surfaced as `db_s_shard_server_part3_test` timing out and being killed
(BF-45092 / BFG-3474784), with the stack stuck in `SharedStateBase::wait` under
`TransactionCoordinator::onCompletion()`.

The cause was a missed wakeup in `NetworkInterfaceMock::setAlarm()`. The `onCancel` callback
did not resolve the alarm's promise; it only recorded the alarm id in `_canceledAlarms`, leaving
resolution to the next pass of `_runReadyNetworkOperations_inlock()`. Because the mock only makes
progress while a test actively drives the network thread, any thread that cancels an alarm and then
blocks waiting on it is never woken. The `TransactionCoordinator` cleanup path does exactly this,
so the test blocked forever on `onCompletion()` after all network responses had been delivered.

SERVER-131498 previously addressed a narrower form of this by looping in
`_runReadyNetworkOperations_inlock()` to drain `_canceledAlarms` after yielding to the executor.
That reduced the window but kept the dependency on the pump, and the hang still reproduced on
master afterwards (locally, at roughly iteration 1400 of
`TransactionCoordinatorTest.RunCommitProducesCommitDecisionOnTwoCommitResponses`).

timeout 660s bazel run +db_s_shard_server_part3_test --   --gtest_filter=TransactionCoordinatorTest.RunCommitProducesCommitDecisionOnTwoCommitResponses   --gtest_repeat=10000   --gtest_break_on_failure