feat(CLOSES open-8261): enhance Google ADK tracing with callback support

- Add token usage capture (prompt_tokens, completion_tokens, total_tokens)
- Support all 6 ADK callbacks (before/after agent, model, tool)
- Enable Google Cloud Trace coexistence (ADK OTel remains active by default)
- Fix callback hierarchy for correct chronological order
- Add recursive step sorting by start_time
- Update example notebook with comprehensive callback demo

Author: viniciusdsmello