test: harden flaky tests that are no longer retried on CI

[turnipdabeets]

💡 Motivation and Context

CI retries failed XCTest cases on the iOS simulator job (#882), but Swift Testing failures aren't retried. Since #915 moved the remaining specs to Swift Testing, these tests now fail CI outright when they flake:

• ExceptionSteps: storage.reset() keeps the event queue, so a previous test's $exception could still be on disk, get sent, and be read as events.first. getSut now deletes this token's app folder first. It's scoped to the token because some tests run two SDKs at once.
• QueueTest:
  • A request that never arrives, or an extra upload, now records an issue instead of indexing out of range. Before, one late request crashed the whole test process.
  • The fixture sets server.batchProjectToken so it only counts its own queue's /batch requests. The stub is process-global, so a stray request from another SDK instance shifted the request count.
• ApplicationViewLayoutPublisher: waitUntil timeout raised from 1s to 5s. It returns as soon as the condition holds, so the higher ceiling only matters on a slow runner.

The replay queue migration test flake is fixed separately in #920.

💚 How did you test it?

• make test filtered to PostHogExceptionStepsTest, PostHogQueueTest and PostHogQueueUploadDispositionTest: 35 tests pass on macOS.
• ApplicationViewLayoutPublisherTest is iOS-only; the change only raises the timeout default. Covered by the test-ios-simulator job.
• SwiftFormat and SwiftLint clean on the changed files.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Written with Claude Code. Test-only changes, so there's no changeset.

🤖 Generated with Claude Code