perf: make signed_integer's is_constant method faster

Signed-off-by: ljedrz <ljedrz@gmail.com>

gadgets/src/signed_integer/int_impl.rs

@@ -82,18 +82,8 @@ macro_rules! int_impl {
             }
 
             fn is_constant(&self) -> bool {
-                let mut constant = true;
-
                 // If any bits of self are allocated bits, return false
-                for bit in &self.bits {
-                    match *bit {
-                        Boolean::Is(ref _bit) => constant = false,
-                        Boolean::Not(ref _bit) => constant = false,
-                        Boolean::Constant(_bit) => {}
-                    }
-                }
-
-                constant
+                self.bits.iter().all(|bit| matches!(bit, Boolean::Constant(_)))
             }
         }
     };