fix: readData in bulk call using messagepack byte wrappers (#11228)

This PR refactors the way we use buffers for O_DIRECT and
to re-use those buffers for messagepack reader writer.

After some extensive benchmarking found that not all objects
have this benefit, and only objects smaller than 64KiB see
this benefit overall.

Benefits are seen from almost all objects from

1KiB - 32KiB

Beyond this no objects see benefit with bulk call approach
as the latency of bytes sent over the wire v/s streaming
content directly from disk negate each other with no
remarkable benefits.

All other optimizations include reuse of msgp.Reader,
msgp.Writer using sync.Pool's for all internode calls.

cmd/erasure-heal_test.go

@@ -99,7 +99,7 @@ func TestErasureHeal(t *testing.T) {
 		readers := make([]io.ReaderAt, len(disks))
 		for i, disk := range disks {
 			shardFilesize := erasure.ShardFileSize(test.size)
-			readers[i] = newBitrotReader(disk, "testbucket", "testobject", shardFilesize, test.algorithm, bitrotWriterSum(writers[i]), erasure.ShardSize())
+			readers[i] = newBitrotReader(disk, nil, "testbucket", "testobject", shardFilesize, test.algorithm, bitrotWriterSum(writers[i]), erasure.ShardSize())
 		}
 
 		// setup stale disks for the test case