feat(storage): sort needles by offset during compaction

seaweed-volume/src/storage/types.rs

@@ -176,7 +176,7 @@ impl From<Size> for i32 {
 ///   [b3][b2][b1][b0]  (big-endian 4 bytes)
 ///
 /// actual_offset = stored_value * 8
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
 pub struct Offset {
     pub b0: u8,
     pub b1: u8,

seaweed-volume/src/storage/volume.rs

@@ -1649,7 +1649,7 @@ impl Volume {
             }
             entries.push((id, nv.offset, nv.size));
         }
-        entries.sort_by_key(|(id, _, _)| *id);
+        entries.sort_by_key(|(_, offset, _)| *offset);
 
         for (id, offset, size) in entries {
             // Progress callback