revert: remove #2351 chunk I/O and object-io crate (phase 7) (#2543)

Co-authored-by: houseme <housemecn@gmail.com>

crates/io-core/src/pool.rs

@@ -17,7 +17,7 @@
 //! Migrated from rustfs-ecstore to provide unified buffer pooling
 //! across rustfs and rustfs-ecstore without cyclic dependencies.
 
-use bytes::{Bytes, BytesMut};
+use bytes::BytesMut;
 use std::mem::ManuallyDrop;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::{Arc, Mutex};
@@ -108,7 +108,6 @@ pub struct BytesPoolMetrics {
 /// A buffer managed by the BytesPool.
 ///
 /// When dropped, the buffer is automatically returned to the pool for reuse.
-#[derive(Debug)]
 pub struct PooledBuffer {
     /// The underlying buffer (ManuallyDrop to allow taking on drop)
     pub buffer: ManuallyDrop<BytesMut>,
@@ -118,45 +117,6 @@ pub struct PooledBuffer {
     _permit: Option<OwnedSemaphorePermit>,
 }
 
-impl PooledBuffer {
-    /// Create a detached pooled buffer from bytes.
-    ///
-    /// This is primarily used for tests and transitional adapters where the
-    /// chunk abstraction needs a pool-shaped owner before a real pool-backed
-    /// producer exists.
-    #[must_use]
-    pub fn from_bytes(bytes: Bytes) -> Self {
-        Self {
-            buffer: ManuallyDrop::new(BytesMut::from(bytes.as_ref())),
-            tier: None,
-            _permit: None,
-        }
-    }
-
-    /// Current visible length of the underlying buffer.
-    #[must_use]
-    pub fn len(&self) -> usize {
-        self.buffer.len()
-    }
-
-    /// Total buffer capacity.
-    #[must_use]
-    pub fn capacity(&self) -> usize {
-        self.buffer.capacity()
-    }
-
-    /// Clear the visible contents while preserving capacity.
-    pub fn clear(&mut self) {
-        self.buffer.clear();
-    }
-
-    /// Returns true when the visible buffer is empty.
-    #[must_use]
-    pub fn is_empty(&self) -> bool {
-        self.buffer.is_empty()
-    }
-}
-
 /// BytesPool configuration.
 ///
 /// Allows customization of buffer sizes and limits for each tier.