Consolidate arena management methods in arena.rs

REORGANIZATION:
- Moved all arena allocation/deallocation methods to arena.rs
- Moved arena statistics and management methods to arena.rs
- Moved unsafe arena access methods to arena.rs
- Removed duplicates from tree_structure.rs

METHODS CONSOLIDATED:
✅ allocate_leaf() & allocate_branch() (already in arena.rs)
✅ deallocate_leaf() & deallocate_branch() (moved from tree_structure.rs)
✅ free_leaf_count() & allocated_leaf_count() (moved from tree_structure.rs)
✅ free_branch_count() & allocated_branch_count() (added to arena.rs)
✅ leaf_utilization() & branch_utilization() (moved from tree_structure.rs)
✅ leaf_arena_stats() & branch_arena_stats() (moved from tree_structure.rs)
✅ set_leaf_next() (moved from tree_structure.rs)
✅ get_leaf_unchecked() & get_branch_unchecked() (moved from tree_structure.rs)

RESULTS:
✅ arena.rs: 436 → 519 lines (+83 lines of arena management)
✅ tree_structure.rs: 226 → 165 lines (-61 lines, focused on structure)
✅ All 317 tests pass - 100% functionality preserved
✅ Clean compilation with no errors
✅ Better logical organization - all arena operations in one place

BENEFITS:
- Single source of truth for arena operations
- Cleaner separation of concerns
- Easier to maintain and extend arena functionality
- More intuitive code organization

Author: KentBeck

rust/src/arena.rs

@@ -299,6 +299,10 @@ pub struct ArenaDebugInfo {
 use crate::types::{BPlusTreeMap, LeafNode, BranchNode};
 
 impl<K: Ord + Clone, V: Clone> BPlusTreeMap<K, V> {
+    // ============================================================================
+    // ARENA ALLOCATION METHODS
+    // ============================================================================
+
     /// Allocate a new leaf node in the arena and return its ID.
     pub fn allocate_leaf(&mut self, leaf: LeafNode<K, V>) -> NodeId {
         self.leaf_arena.allocate(leaf)
@@ -308,6 +312,86 @@ impl<K: Ord + Clone, V: Clone> BPlusTreeMap<K, V> {
     pub fn allocate_branch(&mut self, branch: BranchNode<K, V>) -> NodeId {
         self.branch_arena.allocate(branch)
     }
+
+    /// Deallocate a leaf node from the arena.
+    pub fn deallocate_leaf(&mut self, id: NodeId) -> Option<LeafNode<K, V>> {
+        self.leaf_arena.deallocate(id)
+    }
+
+    /// Deallocate a branch node from the arena.
+    pub fn deallocate_branch(&mut self, id: NodeId) -> Option<BranchNode<K, V>> {
+        self.branch_arena.deallocate(id)
+    }
+
+    // ============================================================================
+    // ARENA STATISTICS AND MANAGEMENT
+    // ============================================================================
+
+    /// Get the number of free leaf nodes in the arena.
+    pub fn free_leaf_count(&self) -> usize {
+        self.leaf_arena.free_count()
+    }
+
+    /// Get the number of allocated leaf nodes in the arena.
+    pub fn allocated_leaf_count(&self) -> usize {
+        self.leaf_arena.allocated_count()
+    }
+
+    /// Get the leaf arena utilization ratio.
+    pub fn leaf_utilization(&self) -> f64 {
+        self.leaf_arena.utilization()
+    }
+
+    /// Get the number of free branch nodes in the arena.
+    pub fn free_branch_count(&self) -> usize {
+        self.branch_arena.free_count()
+    }
+
+    /// Get the number of allocated branch nodes in the arena.
+    pub fn allocated_branch_count(&self) -> usize {
+        self.branch_arena.allocated_count()
+    }
+
+    /// Get the branch arena utilization ratio.
+    pub fn branch_utilization(&self) -> f64 {
+        self.branch_arena.utilization()
+    }
+
+    /// Get statistics for the leaf node arena.
+    pub fn leaf_arena_stats(&self) -> crate::compact_arena::CompactArenaStats {
+        self.leaf_arena.stats()
+    }
+
+    /// Get statistics for the branch node arena.
+    pub fn branch_arena_stats(&self) -> crate::compact_arena::CompactArenaStats {
+        self.branch_arena.stats()
+    }
+
+    /// Set the next pointer of a leaf node in the arena.
+    pub fn set_leaf_next(&mut self, id: NodeId, next_id: NodeId) -> bool {
+        self.get_leaf_mut(id)
+            .map(|leaf| {
+                leaf.next = next_id;
+                true
+            })
+            .unwrap_or(false)
+    }
+
+    // ============================================================================
+    // UNSAFE ARENA ACCESS
+    // ============================================================================
+
+    /// Unsafe fast access to leaf node (no bounds checking)
+    /// SAFETY: Caller must ensure id is valid and allocated
+    pub unsafe fn get_leaf_unchecked(&self, id: NodeId) -> &LeafNode<K, V> {
+        self.leaf_arena.get_unchecked(id)
+    }
+
+    /// Unsafe fast access to branch node (no bounds checking)
+    /// SAFETY: Caller must ensure id is valid and allocated
+    pub unsafe fn get_branch_unchecked(&self, id: NodeId) -> &BranchNode<K, V> {
+        self.branch_arena.get_unchecked(id)
+    }
 }
 
 #[cfg(test)]

rust/src/tree_structure.rs

@@ -138,54 +138,7 @@ impl<K: Ord + Clone, V: Clone> BPlusTreeMap<K, V> {
         }
     }
 
-    // ============================================================================
-    // ARENA STATISTICS AND MANAGEMENT
-    // ============================================================================
-
-    /// Get the number of free leaf nodes in the arena.
-    pub fn free_leaf_count(&self) -> usize {
-        self.leaf_arena.free_count()
-    }
-
-    /// Get the number of allocated leaf nodes in the arena.
-    pub fn allocated_leaf_count(&self) -> usize {
-        self.leaf_arena.allocated_count()
-    }
-
-    /// Get the leaf arena utilization ratio.
-    pub fn leaf_utilization(&self) -> f64 {
-        self.leaf_arena.utilization()
-    }
-
-    /// Get statistics for the leaf node arena.
-    pub fn leaf_arena_stats(&self) -> crate::compact_arena::CompactArenaStats {
-        self.leaf_arena.stats()
-    }
-
-    /// Get statistics for the branch node arena.
-    pub fn branch_arena_stats(&self) -> crate::compact_arena::CompactArenaStats {
-        self.branch_arena.stats()
-    }
-
-    /// Set the next pointer of a leaf node in the arena.
-    pub fn set_leaf_next(&mut self, id: NodeId, next_id: NodeId) -> bool {
-        self.get_leaf_mut(id)
-            .map(|leaf| {
-                leaf.next = next_id;
-                true
-            })
-            .unwrap_or(false)
-    }
-
-    /// Deallocate a leaf node from the arena.
-    pub fn deallocate_leaf(&mut self, id: NodeId) -> Option<LeafNode<K, V>> {
-        self.leaf_arena.deallocate(id)
-    }
-
-    /// Deallocate a branch node from the arena.
-    pub fn deallocate_branch(&mut self, id: NodeId) -> Option<crate::types::BranchNode<K, V>> {
-        self.branch_arena.deallocate(id)
-    }
+    // Arena statistics and management methods moved to arena.rs module
 
     // ============================================================================
     // CHILD LOOKUP HELPERS
@@ -208,19 +161,5 @@ impl<K: Ord + Clone, V: Clone> BPlusTreeMap<K, V> {
         })
     }
 
-    // ============================================================================
-    // UNSAFE ARENA ACCESS
-    // ============================================================================
-
-    /// Unsafe fast access to leaf node (no bounds checking)
-    /// SAFETY: Caller must ensure id is valid and allocated
-    pub unsafe fn get_leaf_unchecked(&self, id: NodeId) -> &LeafNode<K, V> {
-        self.leaf_arena.get_unchecked(id)
-    }
-
-    /// Unsafe fast access to branch node (no bounds checking)
-    /// SAFETY: Caller must ensure id is valid and allocated
-    pub unsafe fn get_branch_unchecked(&self, id: NodeId) -> &crate::types::BranchNode<K, V> {
-        self.branch_arena.get_unchecked(id)
-    }
+    // Unsafe arena access methods moved to arena.rs module
 }