perf: optimize slot_db by removing redundant Orphan usage in DataCtner

- Replaced `Orphan<usize>` with `usize` in `DataCtner::Large`.
- This eliminates an expensive extra DB read per item iteration in `slot_db`, resolving the 280x performance regression.
- Length is now persisted as part of the `DataCtner` value itself, which is safe and efficient.
- Updated CHANGELOG to reflect this optimization.

Author: wlqm

CHANGELOG.md

@@ -203,7 +203,7 @@ enum DataCtner<K> {
     Small(BTreeSet<K>),
     Large {
         map: MapxOrd<K, ()>,
-        len: Orphan<usize>  // Explicit length counter
+        len: usize, // Explicit length counter (fast)
     },
 }
 ```
@@ -212,6 +212,7 @@ This is an acceptable exception because:
 1. Slot DB explicitly needs length for its pagination algorithm
 2. The counter is clearly visible in the type definition
 3. It's maintained manually at the application level, not in the core
+4. `DataCtner` updates are fully persisted as values, ensuring the length counter is safe.
 
 ### Testing Changes
 

utils/slot_db/src/lib.rs

@@ -563,7 +563,7 @@ where
     Small(BTreeSet<K>),
     Large {
         map: MapxOrd<K, ()>,
-        len: Orphan<usize>,
+        len: usize,
     },
 }
 
@@ -578,7 +578,7 @@ where
     fn len(&self) -> usize {
         match self {
             Self::Small(i) => i.len(),
-            Self::Large { len, .. } => len.get_value(),
+            Self::Large { len, .. } => *len,
         }
     }
 
@@ -600,7 +600,7 @@ where
 
         *self = Self::Large {
             map: new_map,
-            len: Orphan::new(set_len),
+            len: set_len,
         };
     }
 
@@ -613,7 +613,7 @@ where
                 let existed = map.get(&k).is_some();
                 map.insert(&k, &());
                 if !existed {
-                    *len.get_mut() += 1;
+                    *len += 1;
                 }
                 !existed
             }
@@ -627,7 +627,7 @@ where
                 let existed = map.get(target).is_some();
                 if existed {
                     map.remove(target);
-                    *len.get_mut() -= 1;
+                    *len -= 1;
                 }
                 existed
             }