HPCC-XXXXX Add OOM detection to postmortem workunit exceptions

[Copilot]

Description

When processes are killed by the OOM (Out Of Memory) killer, dmesg captures the event but this information wasn't surfaced in workunit exceptions. Users had to manually inspect postmortem logs to determine if memory exhaustion caused their failures.

This change adds automatic OOM detection to wutool postmortem:

• Scans dmesg.log for OOM patterns ("Out of memory: Killed process", "oom-kill:", "Memory cgroup out of memory")
• Extracts the complete OOM event line from dmesg
• Creates a workunit exception with severity Error, code 9 (SIGKILL), and the original dmesg details
• Focuses on HPCC processes (thorslave, thormaster, eclagent, roxie) but reports any OOM found

Error handling ensures missing or unreadable dmesg files don't break postmortem processing.

Type of change:

• This change is a bug fix (non-breaking change which fixes an issue).
• This change is a new feature (non-breaking change which adds functionality).
• This change improves the code (refactor or other change that does not change the functionality)
• This change fixes warnings (the fix does not alter the functionality or the generated code)
• This change is a breaking change (fix or feature that will cause existing behavior to change).
• This change alters the query API (existing queries will have to be recompiled)

Checklist:

• My code follows the code style of this project.
  • My code does not create any new warnings from compiler, build system, or lint.
• The commit message is properly formatted and free of typos.
  • The commit message title makes sense in a changelog, by itself.
  • The commit is signed.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly, or...
  • I have created a JIRA ticket to update the documentation.
  • Any new interfaces or exported functions are appropriately commented.
• I have read the CONTRIBUTORS document.
• The change has been fully tested:
  • I have added tests to cover my changes.
  • All new and existing tests passed.
  • I have checked that this change does not introduce memory leaks.
  • I have used Valgrind or similar tools to check for potential issues.
• I have given due consideration to all of the following potential concerns:
  • Scalability
  • Performance
  • Security
  • Thread-safety
  • Cloud-compatibility
  • Premature optimization
  • Existing deployed queries will not be broken
  • This change fixes the problem, not just the symptom
  • The target branch of this pull request is appropriate for such a change.
• There are no similar instances of the same problem that should be addressed
  • I have addressed them here
  • I have raised JIRA issues to address them separately
• This is a user interface / front-end modification
  • I have tested my changes in multiple modern browsers
  • The component(s) render as expected

Smoketest:

• Send notifications about my Pull Request position in Smoketest queue.
• Test my draft Pull Request.

Testing:

Validated pattern matching against multiple OOM scenarios:

• thorslave OOM kill with Memory cgroup out of memory pattern
• eclagent OOM kill with oom-kill: pattern
• Generic process OOM with Out of memory: Killed process pattern
• No false positives on normal dmesg logs

Verified line extraction correctly captures full OOM event details from dmesg.

Original prompt

in the initfiles postmortem scripts, it captures gdb info and dmesg info, then if a workunit id is available, it associates these files to the workunit.
If dmesg is present and it shows that the thorslave process OOM'd, I want to update the workunit exception with that additional information

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