Extend Apple Developer session persistence

[Redth]

Apple Developer download sessions were expiring locally after a short window, forcing repeated Apple ID re-authentication even when Apple still accepted the saved cookies. This keeps the app from interrupting users unnecessarily while still clearing sessions when Apple rejects them.

Changes

• Persist full cookie metadata for Apple Developer download auth and restore legacy saved sessions.
• Extend the local validity window using cookie expiration or a 30-day fallback for session cookies.
• Validate saved sessions before Xcode downloads and clear them only on Apple auth rejection.
• Silently renew restored or near-expiry sessions by calling Apple's session endpoint and saving the refreshed cookie jar.

Validation

• dotnet test tests/MauiSherpa.Core.Tests/MauiSherpa.Core.Tests.csproj --no-restore --verbosity minimal
• dotnet build src/MauiSherpa -f net10.0-maccatalyst --no-restore --verbosity minimal