[Tests] Refactor replay tests to use real filesystem

[gonzaloriestra]

WHY are these changes introduced?

packages/app/src/cli/services/function/replay.test.ts mocked the filesystem (vi.mock('fs') and vi.mock('@shopify/cli-kit/node/fs')) and shared mutable state across tests via beforeAll. Filesystem mocks drift from the real implementation, and shared state makes tests order-dependent and harder to reason about. The CLI testing strategy prefers real files in temporary directories with isolated state per test.

WHAT is this pull request doing?

• Removes the fs and @shopify/cli-kit/node/fs mocks.
• Adds a runTest helper that uses inTemporaryDirectory to give every test its own isolated workspace, function extension, and logs directory.
• Writes real function-run JSON files to disk instead of stubbing readers.
• Normalizes assertions so they tolerate deterministic order and generated identifiers.
• Replaces the beforeAll setup with the per-test helper, eliminating shared mutable state.

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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