various bug fixes

backend/src/lib.rs

@@ -150,6 +150,10 @@ impl Scratch {
         unsafe { &mut *(data as *mut [u8] as *mut Self) }
     }
 
+    pub fn zero(&mut self){
+        self.data.fill(0);
+    }
+
     pub fn available(&self) -> usize {
         let ptr: *const u8 = self.data.as_ptr();
         let self_len: usize = self.data.len();