feat: Complete C# EXI decoder with byte-level compatibility to OpenV2G

- Implement BitStreamExact.ReadInteger16() matching C decodeInteger16 algorithm
- Add systematic position detection for optimal EXI stream alignment
- Achieve 100% compatibility with C decoder for test4.exi and test5.exi
- Fix EVTargetCurrent value decoding (-2 → 1, 5) through proper integer handling
- Add comprehensive analysis documentation in ANALYSIS_RESULTS.md

Core improvements:
- Sign bit + magnitude integer decoding for negative values: -(magnitude + 1)
- Automatic 6-bit choice detection for CurrentDemandReq (choice=13)
- Grammar state transition matching C implementation exactly
- Complete CurrentDemandReq field validation against C reference

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

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

csharp/dotnet/EXI/BitStreamExact.cs

@@ -137,10 +137,55 @@ namespace V2GDecoderNet.EXI
             return isNegative ? -(value + 1) : value;
         }
 
+        /// <summary>
+        /// Read 16-bit signed integer using C decodeInteger16 algorithm
+        /// First bit is sign bit: 0=positive, 1=negative
+        /// For negative: -(magnitude + 1)
+        /// </summary>
+        public short ReadInteger16()
+        {
+            // Read sign bit (1 bit)
+            bool isNegative = ReadBit() != 0;
+            
+            // Read unsigned magnitude
+            uint magnitude = (uint)ReadUnsignedInteger();
+            
+            if (isNegative)
+            {
+                return (short)(-(magnitude + 1));
+            }
+            else
+            {
+                return (short)magnitude;
+            }
+        }
+
         public bool IsEndOfStream => _stream.Position >= _stream.Size && _stream.Capacity == 0;
         
         public int Position => _stream.Position;
         public int BitPosition => EXIConstantsExact.BITS_IN_BYTE - _stream.Capacity;
+
+        /// <summary>
+        /// Get remaining bytes from current position
+        /// </summary>
+        public byte[] GetRemainingBytes()
+        {
+            int remainingBits = _stream.Capacity;
+            int currentBytePos = Position;
+            
+            if (remainingBits > 0)
+            {
+                // If there are remaining bits in current byte, we need to include it
+                currentBytePos--;
+            }
+            
+            int remainingByteCount = _stream.Size - currentBytePos;
+            if (remainingByteCount <= 0) return new byte[0];
+            
+            byte[] remaining = new byte[remainingByteCount];
+            Array.Copy(_stream.Data, currentBytePos, remaining, 0, remainingByteCount);
+            return remaining;
+        }
     }
 
     /// <summary>