fix(kernel): fixed issues enlightened during the review

* Change the location of `max_depth` which is now a impl of Builder
 * Remove the corresponding tests, which will be added in the future
* The test for the depth is now made before the creation of the `Level` struct

elaboration/src/builder/level.rs

@@ -52,6 +52,7 @@ pub enum Builder<'builder> {
 }
 
 impl<'build> Builder<'build> {
+    #[inline]
     fn max_depth(&self) -> usize {
         match self {
             Builder::Zero => 0,