[Tests] Replace filesystem mocks with real temp dir in replay.test.ts

[gonzaloriestra]

WHY are these changes introduced?

The replay.test.ts file was using manual filesystem mocks (vi.mock('fs') and vi.mock('@shopify/cli-kit/node/fs')) to simulate log file discovery and reading. This made the tests brittle and less representative of real behavior, as they were testing the mocks instead of the actual file-discovery and sorting logic.

WHAT is this pull request doing?

This PR refactors packages/app/src/cli/services/function/replay.test.ts to:

• Use testWithTempDir to provide an isolated temporary directory for each test.
• Replace all vi.mock('fs') and @shopify/cli-kit/node/fs mocks with real filesystem operations.
• Introduce a writeFunctionRunFiles helper to populate the temporary directory with deterministic log files.
• Update assertions to reflect the actual sorting behavior of the replay service.

How to test your changes?

Run the unit tests for the replay service:

pnpm --filter @shopify/app vitest run replay.test.ts

Duplicate check

I ran git log --grep="\[Tests\]" --grep="replay.test.ts" --all-match and found no previous PRs targeting this specific test file with these improvements.

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 and added a changeset with pnpm changeset add (N/A for tests)

PR label: Jules (exact casing)

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PR created automatically by Jules for task 7909328793477070431 started by @gonzaloriestra

[google-labs-jules]

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