Fixed GetString on netstandard2

LLama/Extensions/EncodingExtensions.cs

@@ -16,7 +16,7 @@ internal static class EncodingExtensions
         return GetCharCountImpl(encoding, bytes);
     }
 #elif !NET6_0_OR_GREATER && !NETSTANDARD2_1_OR_GREATER
-    #error Target framework not supported!
+#error Target framework not supported!
 #endif
 
     internal static int GetCharsImpl(Encoding encoding, ReadOnlySpan<byte> bytes, Span<char> output)
@@ -47,4 +47,15 @@ internal static class EncodingExtensions
             }
         }
     }
+
+    internal static string GetStringFromSpan(this Encoding encoding, ReadOnlySpan<byte> bytes)
+    {
+        unsafe
+        {
+            fixed (byte* bytesPtr = bytes)
+            {
+                return encoding.GetString(bytesPtr, bytes.Length);
+            }
+        }
+    }
 }

LLama/Native/SafeLlamaModelHandle.cs

@@ -3,6 +3,8 @@ using System.Buffers;
 using System.Collections.Generic;
 using System.Text;
 using LLama.Exceptions;
+using LLama.Extensions;
+using EncodingExtensions = LLama.Extensions.EncodingExtensions;
 
 namespace LLama.Native
 {
@@ -259,12 +261,12 @@ namespace LLama.Native
                     var keyBytes = MetadataKeyByIndex(i, dest.AsMemory());
                     if (keyBytes == null)
                         continue;
-                    var key = Encoding.UTF8.GetString(keyBytes.Value.Span);
+                    var key = Encoding.UTF8.GetStringFromSpan(keyBytes.Value.Span);
 
                     var valBytes = MetadataValueByIndex(i, dest.AsMemory());
                     if (valBytes == null)
                         continue;
-                    var val = Encoding.UTF8.GetString(valBytes.Value.Span);
+                    var val = Encoding.UTF8.GetStringFromSpan(valBytes.Value.Span);
 
                     result[key] = val;
                 }