MDEV-40222 Prevent MTR hang when waiting for wsrep_ready

[mariadb-TeemuOllakka]

A query against a server that is up but wedged can connect yet never return, so the loop-count bound in wait_wsrep_ready() did not actually limit the wait and MTR could hang until the suite timeout fired.

Add an optional $timeout to run_query_output(): the mysql client is now spawned via My::SafeProcess->new and waited for with wait_one($timeout), killing the client and returning non-zero if it does not finish in time.

Bound wait_wsrep_ready() by a wall-clock deadline (start_timer) instead of a loop count, and pass the remaining time to each query so no single hung client can exceed the overall server startup budget.

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[gemini-code-assist]

Code Review

This pull request introduces a timeout mechanism to run_query_output in mariadb-test-run.pl to prevent MTR from hanging indefinitely when querying a wedged server. It replaces the loop-based wait with a wall-clock deadline and uses My::SafeProcess to monitor and kill hung clients if they exceed the remaining startup budget. The review feedback highlights a potential issue where an undefined $timeout argument could trigger Perl warnings or cause premature process termination, and suggests conditionally calling wait_one based on whether $timeout is defined.

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[gemini-code-assist]

If $timeout is not passed to run_query_output (which is the case for other callers or if it is omitted), $timeout will be undef. Passing undef to $proc->wait_one($timeout) can cause two issues:\n\n1. It may trigger a Perl warning about an uninitialized value.\n2. If wait_one treats undef as 0 (non-blocking poll), it will return 1 immediately because the process is still running, causing the client to be killed prematurely.\n\nTo prevent this, we should explicitly check if $timeout is defined before passing it to wait_one.

  # wait_one() returns 1 while the process is still running,
  # in which case we kill the hung client.
  if (defined $timeout ? $proc->wait_one($timeout) : $proc->wait_one())
  {
    $proc->kill();
    return 1;
  }

  return $proc->exit_status();