fix: adjust finalBuffer slicing to use dynamic prefix length

Author: Panayiotis Savva

src/Base58.cs

@@ -188,7 +188,7 @@ public bool TryDecodeCheck(
             return false;
         }
 
-        var finalBuffer = buffer[1..^Sha256.DigestBytes];
+        var finalBuffer = buffer[prefix.Length..^Sha256.DigestBytes];
         finalBuffer.CopyTo(payload);
         payloadBytesWritten = finalBuffer.Length;
         return true;