Optimize reading binary strings

Fixes #98

Author: xPaw

ValveKeyValue/ValveKeyValue/Deserialization/KeyValues1/KV1BinaryReader.cs

@@ -1,3 +1,4 @@
+using System.Buffers;
 using System.Text;
 using ValveKeyValue.Abstraction;
 using ValveKeyValue.KeyValues1;
@@ -84,7 +85,7 @@ string ReadKeyForNextValue()
                 return stringTable[index];
             }
 
-            return Encoding.UTF8.GetString(ReadNullTerminatedBytes());
+            return ReadNullTerminatedUtf8String();
         }
 
         void ReadValue(KV1BinaryNodeType type)
@@ -102,7 +103,7 @@ void ReadValue(KV1BinaryNodeType type)
 
                 case KV1BinaryNodeType.String:
                     // UTF8 encoding is used for string values
-                    value = new KVObjectValue<string>(Encoding.UTF8.GetString(ReadNullTerminatedBytes()), KVValueType.String);
+                    value = new KVObjectValue<string>(ReadNullTerminatedUtf8String(), KVValueType.String);
                     break;
 
                 case KV1BinaryNodeType.WideString:
@@ -137,16 +138,41 @@ void ReadValue(KV1BinaryNodeType type)
             listener.OnKeyValuePair(name, value);
         }
 
-        byte[] ReadNullTerminatedBytes()
+        string ReadNullTerminatedUtf8String()
         {
-            using var mem = new MemoryStream();
-            byte nextByte;
-            while ((nextByte = reader.ReadByte()) != 0)
+            var buffer = ArrayPool<byte>.Shared.Rent(32);
+
+            try
             {
-                mem.WriteByte(nextByte);
+                var position = 0;
+
+                do
+                {
+                    var b = reader.ReadByte();
+
+                    if (b <= 0) // null byte or stream ended
+                    {
+                        break;
+                    }
+
+                    if (position >= buffer.Length)
+                    {
+                        var newBuffer = ArrayPool<byte>.Shared.Rent(buffer.Length * 2);
+                        Buffer.BlockCopy(buffer, 0, newBuffer, 0, buffer.Length);
+                        ArrayPool<byte>.Shared.Return(buffer);
+                        buffer = newBuffer;
+                    }
+
+                    buffer[position++] = b;
+                }
+                while (true);
+
+                return Encoding.UTF8.GetString(buffer[..position]);
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
             }
-
-            return mem.ToArray();
         }
 
         void DetectMagicHeader()