[PR] [SPARK-59985][4.1][ML][PYTHON] Fix malformed warning in TorchDistributor when the log streaming server fails to start [spark]

["firasbouzazi (via GitHub)" <gi...@apache.org>]

firasbouzazi opened a new pull request, #59383:
URL: https://github.com/apache/spark/pull/59383

   ### What changes were proposed in this pull request?
   
   Backport of #59242 to branch-4.1.
   
   Fix the warning that `TorchDistributor._run_distributed_training` emits when the log streaming server fails to start. The message had a stray comma, so the error text was passed to `logger.warning` as an extra positional argument, and formatting the record raised `TypeError: not all arguments converted during string formatting`. The warning now uses a single format string with the exception as its argument.
   
   The cherry-pick conflicted only in the test file, where master has a neighbouring test that is not on this branch. Adaptations to the test:
   - The test does not assert `log_streaming_auth_secret`, which does not exist on this branch.
   - The test file now imports `MagicMock`, which it did not import on this branch.
   
   ### Why are the changes needed?
   
   Users see a `--- Logging error ---` traceback instead of the one-line warning explaining why worker logs are missing (or nothing, with `logging.raiseExceptions = False`).
   
   ### Does this PR introduce _any_ user-facing change?
   
   Yes. When the log streaming server fails to start, users get the intended warning instead of a logging error traceback.
   
   ### How was this patch tested?
   
   `test_log_streaming_server_start_failure_warns` (added in #59242) fails with the `TypeError` above without the fix and passes with it on this branch. `TorchDistributorBaselineUnitTests` passes.
   
   ### Was this patch authored or co-authored using generative AI tooling?
   
   Generated-by: Claude Code
   


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