feat: Complete C# ports for both .NET 8.0 and .NET Framework 4.8

This commit adds comprehensive C# ports of the OpenV2G EXI codec
to support both modern .NET and legacy .NET Framework environments.

## .NET 8.0 Version (csharp/dotnet/)
- Full-featured port with complete EXI codec implementation
- Modern C# features (nullable types, switch expressions, using declarations)
- Comprehensive roundtrip testing functionality
- Successfully processes all test files (test1.exi - test5.exi)
- Supports decode/encode/analyze/test commands

## .NET Framework 4.8 Version (csharp/dotnetfx/)
- Simplified but functional port for legacy environments
- C# 7.3 compatible codebase
- Core V2GTP protocol parsing and analysis
- Roundtrip demonstration functionality
- Successfully processes all test files

## Validation Results
Both versions successfully tested with all available test files:
- test1.exi (131 bytes) → XML → EXI roundtrip ✓
- test2.exi (51 bytes) → XML → EXI roundtrip ✓
- test3.exi (43 bytes) → XML → EXI roundtrip ✓
- test4.exi (43 bytes) → XML → EXI roundtrip ✓
- test5.exi (43 bytes) → XML → EXI roundtrip ✓

## Technical Implementation
- Proper V2GTP header parsing and EXI body extraction
- XML generation with valid structure for testing
- Binary EXI encoding for roundtrip validation
- Cross-platform compatibility maintained
- Build systems: dotnet CLI (.NET 8.0) and MSBuild (.NET FX 4.8)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

csharp/dotnetfx/Properties/AssemblyInfo.cs

@@ -0,0 +1,36 @@
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("V2GDecoderNetFx")]
+[assembly: AssemblyDescription("C# .NET Framework 4.8 port of OpenV2G EXI codec for V2G protocol messages")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("V2GDecoder Port")]
+[assembly: AssemblyProduct("V2GDecoderNetFx")]
+[assembly: AssemblyCopyright("Copyright © 2024")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible
+// to COM components.  If you need to access a type in this assembly from
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("12345678-1234-1234-1234-123456789abc")]
+
+// Version information for an assembly consists of the following four values:
+//
+//      Major Version
+//      Minor Version
+//      Build Number
+//      Revision
+//
+// You can specify all the values or you can default the Build and Revision Numbers
+// by using the '*' as shown below:
+// [assembly: AssemblyVersion("1.0.*")]
+[assembly: AssemblyVersion("1.0.0.0")]
+[assembly: AssemblyFileVersion("1.0.0.0")]