Performance: VarHandle little-endian access in packet buffers

{ReadableByteBuf}} and Writer decode and encode integers with shift-and-mask sequences (about 40 sites). MethodHandles.byteArrayViewVarHandle(int[].class, ByteOrder.LITTLE_ENDIAN) and the long[] / short[] equivalents give single bounds-checked intrinsic reads and writes.

• Introduce VarHandle-based readShort / readInt / readLong and writeShort / writeInt / writeLong, keeping the current API.
• Benchmark with the existing JMH bench profile (select of int and long columns, batch inserts) before and after, and record the numbers in this ticket.
• Evaluate java.lang.ref.Cleaner for pool and query-timeout scheduler shutdown instead of the current explicit lifecycle code, only where it simplifies without adding latency.