refactor: fix last 4 clippy warnings (if_same_then_else, too_many_arguments)

Reduced warnings from 4 to 0 — cookbook lib is now clippy-clean.

Changes:
- if_same_then_else (1): combined identical Ok(list) branches with || in
  staged_pkg.rs new_recursive()
- too_many_arguments (3): added #[allow(clippy::too_many_arguments)] with
  justification comments (required by AGENTS.md WARNING POLICY) on
  display_tree_entry, walk_tree_entry, new_recursive — params are genuinely
  independent display/traversal/recursion options

Verification: cargo check ✅, cargo test --lib ✅ 38/38, cargo clippy 0 warnings.

src/cook/tree.rs

@@ -16,6 +16,7 @@ pub enum WalkTreeEntry<'a> {
     Missing,
 }
 
+#[allow(clippy::too_many_arguments)] // params are independent display options
 pub fn display_tree_entry(
     package_name: &PackageName,
     recipe_map: &HashMap<&PackageName, &CookRecipe>,
@@ -39,6 +40,7 @@ pub fn display_tree_entry(
     )
 }
 
+#[allow(clippy::too_many_arguments)] // params are independent traversal options
 pub fn walk_tree_entry(
     package_name: &PackageName,
     recipe_map: &HashMap<&PackageName, &CookRecipe>,

src/recipe.rs

@@ -275,6 +275,7 @@ impl CookRecipe {
         Self::new(name, dir.to_path_buf(), recipe)
     }
 
+    #[allow(clippy::too_many_arguments)] // params are independent recursion flags
     fn new_recursive(
         names: &[PackageName],
         recurse_build_deps: bool,

src/staged_pkg.rs

@@ -97,9 +97,7 @@ pub fn new_recursive(
         return Ok(vec![]);
     }
     let (list, map) = new_recursive_nonstop(names, recursion);
-    if nonstop && !list.is_empty() {
-        Ok(list)
-    } else if !nonstop && map.len() == list.len() {
+    if (nonstop && !list.is_empty()) || (!nonstop && map.len() == list.len()) {
         Ok(list)
     } else {
         let (_, res) = map.into_iter().find(|(_, v)| v.is_err()).unwrap();