optimize startup sequence performance (#19009)

- bucket metadata does not need to look for legacy things
  anymore if b.Created is non-zero

- stagger bucket metadata loads across lots of nodes to
  avoid the current thundering herd problem.

- Remove deadlines for RenameData, RenameFile - these
  calls should not ever be timed out and should wait
  until completion or wait for client timeout. Do not
  choose timeouts for applications during the WRITE phase.

- increase R/W buffer size, increase maxMergeMessages to 30

internal/grid/connection.go

@@ -175,8 +175,8 @@ func (c ContextDialer) DialContext(ctx context.Context, network, address string)
 
 const (
 	defaultOutQueue    = 10000
-	readBufferSize     = 16 << 10
-	writeBufferSize    = 16 << 10
+	readBufferSize     = 32 << 10 // 32 KiB is the most optimal on Linux
+	writeBufferSize    = 32 << 10 // 32 KiB is the most optimal on Linux
 	defaultDialTimeout = 2 * time.Second
 	connPingInterval   = 10 * time.Second
 	connWriteTimeout   = 3 * time.Second
@@ -654,7 +654,7 @@ func (c *Connection) connect() {
 				fmt.Printf("%v Connecting to %v: %v. Retrying.\n", c.Local, toDial, err)
 			}
 			sleep := defaultDialTimeout + time.Duration(rng.Int63n(int64(defaultDialTimeout)))
-			next := dialStarted.Add(sleep)
+			next := dialStarted.Add(sleep / 2)
 			sleep = time.Until(next).Round(time.Millisecond)
 			if sleep < 0 {
 				sleep = 0
@@ -950,7 +950,7 @@ func (c *Connection) handleMessages(ctx context.Context, conn net.Conn) {
 				cancel(ErrDisconnected)
 				return
 			}
-			if cap(msg) > readBufferSize*8 {
+			if cap(msg) > readBufferSize*4 {
 				// Don't keep too much memory around.
 				msg = nil
 			}