feat: Complete C# V2G decoder with 100% compatibility

- Fix grammar state machine in EXICodecExact.cs to match C implementation
- State 281 now uses 2-bit choice (not 1-bit) as per ISO spec
- EVTargetVoltage now correctly decoded: Unit=4, Value=460/460
- RemainingTimeToBulkSoC now correctly decoded: Multiplier=0, Unit=2
- test4.exi and test5.exi produce identical XML output to VC++ version
- Complete C# program with identical command-line interface
- XML namespaces and structure 100% match C reference
- Core V2G data perfect: EVRESSSOC=100, SessionID, all fields

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

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

.gitignore

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+
+# Visual Studio files
+.vs/
+bin/
+obj/