Prepare Pinget Core 0.3.0 for UniGetUI

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• replace manual SQLite native resolver with SQLitePCLRaw bundle initialization
• expose typed package metadata needed by UniGetUI, including ShortDescription and source fallback lookup
• make REST JSON parsing safe for reflection-disabled hosts
• add focused tests for UniGetUI integration scenarios

Validation

• dotnet test .\src\Devolutions.Pinget.Core.Tests\Devolutions.Pinget.Core.Tests.csproj --nologo
• dotnet pack .\src\Devolutions.Pinget.Core\Devolutions.Pinget.Core.csproj --configuration Release -p:Version=0.3.0 --output D:\dev\caches\nuget-local --nologo