[Tests] Remove filesystem mocks in app-logs-polling.test.ts

[gonzaloriestra]

WHY are these changes introduced?

Following the standardized approach for file system interactions in unit tests, this PR removes global filesystem mocks in app-logs-polling.test.ts to improve test reliability and maintainability.

WHAT is this pull request doing?

• Removed vi.mock('@shopify/cli-kit/node/fs') from packages/app/src/cli/services/dev/processes/app-logs-polling.test.ts.
• Updated tests to use inTemporaryDirectory from @shopify/cli-kit/node/fs for tests that trigger directory creation.
• Updated assertions to use fileExistsSync on real paths instead of checking mock calls on mkdir.

How to test your changes?

CI

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 9193237525126123010 started by @gonzaloriestra

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