Add comprehensive test suite for Bushel demo

[leogdion]

Overview

Add full test coverage for the Bushel CloudKit demo to ensure reliability and serve as examples for users learning MistKit.

Test Coverage Needed

Unit Tests

• Data Source Fetchers: IPSWFetcher, XcodeReleasesFetcher, SwiftVersionFetcher, MESUFetcher, MrMacintoshFetcher, TheAppleWikiFetcher response parsing
• CloudKit Integration: BushelCloudKitService initialization, RecordBuilder field mapping, Batch operation chunking logic
• Data Pipeline: Deduplication logic, Multi-source merging, Dependency ordering

Integration Tests

• Mock CloudKit Tests: Sync/export operations with mock service, Error handling for CloudKit failures
• Edge Cases: Network failures, Malformed API responses, Missing/invalid data fields, Partial batch failures

Benefits

• Ensures code reliability
• Serves as usage examples for developers
• Demonstrates MistKit testing patterns
• Prevents regressions during updates

References

• Main MistKit test suite for patterns
• Swift Testing framework documentation