Evaluate in place expressions

This solution gives similar performance results than the tree based one,
mostly because of the intermediate vectors.

board-shared/src/tile.rs

@@ -68,6 +68,15 @@ pub enum Operator {
     Divide,
 }
 
+impl Operator {
+    pub fn precedence(&self) -> u8 {
+        match self {
+            Operator::Add | Operator::Subtract => 1,
+            Operator::Multiply | Operator::Divide => 2,
+        }
+    }
+}
+
 impl fmt::Display for Operator {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {