Fix FakeAsync usage in last_online_reporting tests

[nilsreichardt]

Motivation

• Tests using FakeAsync were effectively passing unconditionally because microtasks and debounced timers were not driven correctly, hiding regressions.
• The tests also used an inconsistent debounce duration which made them harder to reason about.

Description

• Use a single debounceTime constant and pass it into LastOnlineReporter.internal so tests and setup are consistent.
• Run FakeAsync().run with synchronous closures and explicitly call fakeAsync.flushMicrotasks() and fakeAsync.elapse(...) to properly drive timers and microtasks.
• Trigger the backend error path in the crash-logging test by setting backend.shouldThrow = true and replace pumpEventQueue/async awaits with flushMicrotasks or hasListener checks to validate subscription cleanup.

Testing

• Executed fvm flutter test lib/last_online_reporting/test/last_online_reporting_test.dart and all tests passed.

---

Codex Task

[gemini-code-assist]

Code Review

This pull request significantly improves the reliability of tests for LastOnlineReporter by correcting the usage of FakeAsync. The changes properly use flushMicrotasks and elapse to manage asynchronous operations in tests, remove incorrect async/await patterns, and fix logic errors that caused tests to pass unconditionally. Using a constant for the debounce time also improves consistency. Overall, these are excellent changes that make the test suite more robust. The minor suggestion provided is still valid.

[gemini-code-assist]

For consistency with the other tests in this file, it's good practice to flush microtasks after calling startReporting() to ensure any initial events are processed before proceeding with the test's assertions. This also makes the test more robust against future changes to startReporting().

Suggested change

	lastOnlineReporter.startReporting();
	await pumpEventQueue();
	expect(lifecycleChanges.hasListener, true);
	lastOnlineReporter.startReporting();
	fakeAsync.flushMicrotasks();
	expect(lifecycleChanges.hasListener, true);

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