Rust: Add validation to decode

mojo/public/rust/src/bindings/encoding.rs

Index: mojo/public/rust/src/bindings/encoding.rs
diff --git a/mojo/public/rust/src/bindings/encoding.rs b/mojo/public/rust/src/bindings/encoding.rs
index 1cb3a91c297d2e6604f1d469352286f66a2b6870..41d9c8ad1983371902ceea4e3c3e58c7743d7f5c 100644
--- a/mojo/public/rust/src/bindings/encoding.rs
+++ b/mojo/public/rust/src/bindings/encoding.rs
@@ -41,6 +41,13 @@ impl Bits {
         1 << (self.0 & 7)
     }
 
+    pub fn checked_mul(self, val: usize) -> Option<Bits> {
+        match val.checked_mul(self.0) {
+            Some(result) => Some(Bits(result)),
+            None => None,
+        }
+    }
+
     /// Align the bits to some number of bytes.
     pub fn align_to_bytes(&mut self, bytes: usize) {
         self.0 = util::align_bytes(self.0, 8 * bytes);