Prevent using str type arg in int.from_bytes (#958)

* Prevent using str type arg in int.from_bytes

* Add NotNull attribute to from_bytes

Co-authored-by: Stéphane Lozier <slozier@users.noreply.github.com>

Author: BCSharp

Src/IronPython/Runtime/Bytes.cs

@@ -164,6 +164,8 @@ internal static Bytes FromObject(CodeContext context, object? o) {
                 return (Bytes)o;
             } else if (TryInvokeBytesOperator(context, o, out Bytes? res)) {
                 return res;
+            } else if (o is string || o is ExtensibleString) {
+                throw PythonOps.TypeError("cannot convert unicode object to bytes");
             } else {
                 return new Bytes(ByteOps.GetBytes(o, useHint: true, context).ToArray());
             }

Src/IronPython/Runtime/Operations/IntOps.cs

@@ -528,7 +528,7 @@ public static Bytes to_bytes(Int32 value, int length, string byteorder, bool sig
             return Bytes.Make(res.ToArray());
         }
 
-        public static BigInteger from_bytes([BytesLike]IList<byte> bytes, string byteorder, bool signed=false) {
+        public static BigInteger from_bytes([NotNull, BytesLike]IList<byte> bytes, string byteorder, bool signed=false) {
             // TODO: signed should be a keyword only argument
             // TODO: return int when possible?