[train] update failure policy log message

[matthewdeng]

Description

Update formatting of FailurePolicy log message to be more readable.

Additional information

Before:

[FailurePolicy] Decision: FailureDecision.RAISE, Error source: controller, Error count / maximum errors allowed: 1/0, Error: Training failed due to controller error:
Worker group is not active. Call WorkerGroup.create() to create a new worker group.

After:

[FailurePolicy] RAISE
  Source: controller
  Error count: 1 (max allowed: 0)

Training failed due to controller error:
Worker group is not active. Call WorkerGroup.create() to create a new worker group.

[gemini-code-assist]

Code Review

This pull request successfully improves the readability of the failure policy log message by reformatting it into a multi-line string. The change is clear and effective. I have provided one suggestion to use a single multi-line f-string, which could make the code that generates the message even more readable and idiomatic.

[gemini-code-assist]

For improved readability and to make the multi-line string structure more explicit, consider using a single triple-quoted f-string. This avoids repeating f"" and using explicit newline characters (\n), making the log message template easier to read and maintain.

f"""[FailurePolicy] {decision.value}
  Source: {error_source}
  Error count: {error_count} (max allowed: {retry_limit})

{training_failed_error}"""