1. Remove unused import Mock from test_trace_serialization.py
2. Remove unused import safe_serialize_to_dict from test_trace_serialization.py
3. Fix LLM event tools data being silently excluded: Remove 'tools' from
TRACE_EXCLUDE_FIELDS since LLMCallStartedEvent.tools is a lightweight
list of tool schemas, not heavy Agent.tools objects. Agent.tools is
already excluded explicitly in _build_crew_started_data.
4. Remove dead code: complex_events class variable from TraceCollectionListener
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>