Add size hint for SliceIter

src/root.zig

@@ -419,6 +419,10 @@ pub fn SliceIter(comptime T: type, comptime item_type: SliceItemType) type {
                 .ptr, .const_ptr => &self.slice[self.i],
             };
         }
+
+        pub fn sizeHint(self: *const Self) usize {
+            return self.slice.len;
+        }
     };
 }