Upgrade project to .NET 6 and add GitHub Actions workflow

[CodeMangler]

This commit brings several major updates to the EventLogAnalyzer project:

1. Framework Upgrade:

   • All projects (Console Client, EventLog, UnitTests) have been upgraded from .NET Framework 2.0 to .NET 6.
   • Project files (.csproj) have been converted to the modern SDK-style format.
   • The NUnit testing framework reference in UnitTests has been updated to use NuGet packages (NUnit 3.13.3, NUnit3TestAdapter 4.5.0, Microsoft.NET.Test.Sdk 17.3.2).

2. Build System:

   • The primary build mechanism is now dotnet build using the EventLogAnalyzer.sln solution file.
   • Obsolete build scripts (build.bat, eventloganalyzer.build) have been removed.
   • The System.Diagnostics.EventLog NuGet package (v6.0.0) was added to EventLog.csproj to resolve compatibility issues with EventLogEntryType.
   • Fixed build issues related to duplicate EmbeddedResources and assembly attributes in Console Client.csproj.

3. GitHub Actions CI:

   • A new GitHub Actions workflow (.github/workflows/dotnet-build.yml) has been added.
   • This workflow builds and tests the solution on windows-latest (due to Windows-specific EventLog APIs) for pushes and pull requests to the main branch.

4. Codebase Cleanup:

   • Removed obsolete solution files (EventLog Analyzer - VS 2005.sln, EventLog Analyzer - VS 2008.sln).
   • Removed the local lib/nunit.framework.dll.
   • Removed EventLog/EventLog.idc.
   • Removed the Output/ directory (build artifacts) from source control and added it to .gitignore.
   • Added .vs/ to .gitignore.
   • Deleted AssemblyInfo.cs files as their content is now managed by the SDK-style projects.

5. Documentation:

   • README.md has been updated with new build instructions for .NET 6.