- Implemented new CSharpLanguageServer class using Microsoft's official C# language server
- Downloads Microsoft.CodeAnalysis.LanguageServer NuGet package (requires .NET 9)
- Supports direct download from NuGet API with fallback to package managers
- Uses platform-specific runtime packages (linux-x64, win-x64, osx-x64, etc.)
- Caches downloaded language server in ~/.cache/serena/language-servers/csharp/
- Added basic tests for C# language server functionality
- Updated SolidLanguageServer.create to use new implementation
- Removed old OmniSharp implementation
Note: Full language server tests are skipped as they require .NET 9 runtime