Consolidate withTemporaryDirectory test helper

[sebsto]

Consolidates duplicate withTemporaryDirectory helper implementations into a single shared helper in TestHelpers.swift.

Changes:

• Moved withTemporaryDirectory to shared TestHelpers.swift
• Removed duplicate implementations from FileHandlerTests, ConfigHandlerTests, and DownloadDelegateTests
• Added both sync and async variants with shared implementation
• Extracted common logic into private createTemporaryDirectory helper
• Updated all test files to use the global helper

This reduces code duplication and makes test helpers more maintainable. All tests compile and pass successfully.

[amazon-q-developer]

The consolidation of withTemporaryDirectory helper functions is well-executed. The refactoring successfully eliminates code duplication across test files while maintaining identical functionality. The shared implementation in TestHelpers.swift properly handles both synchronous and asynchronous test cases with appropriate cleanup using defer blocks. All test files have been correctly updated to use the global helper. No blocking issues found.

---

You can now have the agent implement changes and create commits directly on your pull request's source branch. Simply comment with /q followed by your request in natural language to ask the agent to make changes.