Use .inMemory UserDefaults in SidebarPersistenceMigratorTests

[sbertix]

Summary

• SidebarPersistenceMigratorTests was overriding $0.defaultAppStorage = UserDefaults(suiteName: "\(#function).\(UUID().uuidString)")!, which cfprefsd persisted to ~/Library/Preferences/ — leaking ~16 plists per test run (thousands after many local/CI runs).
• swift-sharing ships UserDefaults.inMemory for exactly this case: on macOS 14+/iOS 17+ it prefixes the suite name with NSTemporaryDirectory(), so cfprefsd writes the plist to /var/folders/.../T/co.pointfree.Sharing.<UUID>.plist (auto-reaped by the OS) instead of the user-visible ~/Library/Preferences/.
• Net -15 lines: no helper functions, no per-test defer, no UUID-suffix gymnastics. Every leaking call site is now $0.defaultAppStorage = .inMemory.

Verification

• make test passes (1097 tests, 78 suites).
• Before: each make test run added 16 fresh plists to ~/Library/Preferences/ (with method-name + UUID filenames). After: 0 new files there; 16 fresh files in NSTemporaryDirectory() instead, where the OS handles cleanup.

Cleaning up the historical leaks

This PR stops the bleeding but doesn't touch the plists already sitting in your ~/Library/Preferences/ from prior runs of this (and earlier, since-deleted) test classes. Run locally to clean them up:

# Dry run — count what would be deleted (test-pattern plists only, never bundle-ID plists)
find ~/Library/Preferences -maxdepth 1 -type f \
  \( -name "*Tests.*.plist" -o -name "*\(\).plist" -o -name "*\(\).*.plist" \) | wc -l

# Delete them
find ~/Library/Preferences -maxdepth 1 -type f \
  \( -name "*Tests.*.plist" -o -name "*\(\).plist" -o -name "*\(\).*.plist" \) -delete

# Flush cfprefsd so it doesn't re-write any stragglers from memory
killall cfprefsd

The patterns target only Swift-test-shaped filenames (<ClassName>Tests.<...>.plist, <method>().plist, <method>().<UUID>.plist) — they will never match real app/system preference files, which use reverse-DNS bundle IDs (com.apple.*, com.microsoft.*, etc.).

Test plan

• make test green locally
• make check (swift-format + swiftlint) green
• Two consecutive test runs verified: 0 new files in ~/Library/Preferences/

[tuist]

🛠️ Tuist Run Report 🛠️

Builds 🔨

Scheme	Status	Duration	Commit
supacode	✅	1m 56s	fd87e02d0