HDDS-16419. Avoid nested datanode failover in GetBlock and ReadChunk

[symious]

What changes were proposed in this pull request?

ContainerProtocolCalls#getBlock and #readChunk fail over between datanodes
via tryEachDatanode. For each datanode, they call
XceiverClientSpi#sendCommand(request, validators). In XceiverClientGrpc this
goes to sendCommandWithRetry, which again tries every datanode of the
pipeline. As a result:

• every datanode is contacted N times, so a single call can take
  N × N × ozone.client.read.timeout before failing, and a read can take
  read.max.retries × N × N × read.timeout;
• the request built for datanode A (datanodeUuid, EC replica index) may be
  sent to datanode B.

This PR makes tryEachDatanode the only failover layer for these two commands:

• XceiverClientSpi
  • Add sendCommand(request, validators, datanode), which sends the command
    to the given datanode only. The default implementation falls back to
    sendCommand(request, validators), so Ratis and short-circuit clients are
    unchanged.
  • Add getDatanodesInOrder(blockID, cmdType). The default implementation
    returns the datanodes in Pipeline#getClosestNode order, which is the
    current behavior of tryEachDatanode.
• XceiverClientGrpc
  • Extract the single-datanode part of sendCommandWithRetry into
    sendCommandToDatanode: send, run validators, update the GetBlock
    datanode cache. Both the existing retry loop and the new
    sendCommand(request, validators, datanode) use it.
  • getDatanodesInOrder reuses sortDatanodes, so the datanode order
    (leader / cached GetBlock datanode first, non-IN_SERVICE last,
    topology-aware or shuffled) is the same as before.
• ContainerProtocolCalls
  • tryEachDatanode iterates over getDatanodesInOrder.
  • The per-datanode GetBlock/ReadChunk calls use the new single-datanode
    sendCommand.

Other commands (listBlock, readSmallFile, ...) still use the inner failover
and are not affected.

After this change, the worst case for a read is
read.max.retries × N × read.timeout.

Note: getBlockFromDatanode (used by ozone debug replicas chunk-info) now
really queries only the given datanode. Before this change it could silently
return the result from another datanode.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16419

How was this patch tested?

• TestXceiverClientGrpc
  • testGetBlockRetryAlNodes / testReadChunkRetryAllNodes now assert that
    each datanode is contacted exactly once (previously N² calls), and that
    the request's datanodeUuid matches the datanode it is sent to.
  • New testReadChunkRetryNextNodeOnShortRead: a short read from the first
    datanode is retried on the next datanode.
  • Existing ordering tests (leader, topology, IN_SERVICE first, connection
    reuse after GetBlock) pass unchanged.
• TestChunkInputStream, TestBlockInputStream pass.

[yandrey321]

lgtm