M3/logger override minimal

[guru-code-expert]

Summary

This PR adds minimal logger robustness needed for M3 integration with Trace-Bench UI/CLI.

Changes

• Add NullLogger support.
• Make load_logger() tolerant of none/null/off/disabled.
• Unknown logger names now warn and fall back safely.
• If a trainer class rejects logger=..., retry without logger (warn, continue).
• Fix save_train_config wrapper to handle positional args correctly.

Validation

• pytest -q tests/unit_tests/test_logger_override.py passes.
• Verified compatibility with Trace-Bench logger override flow.

[doxav]

Hi Asad,

This PR could be totally reduced because we should not change examples and some modifications could be in Trace-Bench.

Please remove all example-file smoke guards from OpenTrace, keep only the search_template.py fix, and move the rest into Trace-Bench.

• Keep the save_train_config positional-args fix in search_template.py, and make Trace-Bench explicitly excludes SequentialUpdate, SequentialSearch, and BeamSearch if not fixed.

I propose you to:

1. Rewrite tests/m1/test_opentrace_examples_smoke.py

   • remove env var injection
   • remove runpy.run_path(...)
   • replace with py_compile smoke

2. Add a local no-op logger in Trace-Bench

   • trace_bench/null_logger.py

3. Use that no-op logger when logger override is "none"

   • in Trace-Bench runtime resolution / runner path

4. Handle error in SequentialUpdate, SequentialSearch, BeamSearch if Trace version does not have the search_template.py fix