Add unit and E2E testing steps and examples for OTel tracing and metrics

[morgan-wowk]

Objective

Give contributors clear steps and examples of unit and E2E testing OTel traces and metrics (instruments).

[maxy-shpfy]

🤖 Auto-triage assigned priority P3

The issue involves adding unit and E2E testing steps and examples for OTel tracing and metrics, which is a code quality improvement and enhancement task. It does not impact essential functionality or address any urgent project requirements, nor does it involve user-reported issues or significant bugs.

Key factors:
• code quality improvement
• observability enhancement
• not essential for current cycle

📋 P3 Priority: Nice-to-have or future work.

This priority was determined by AI analysis with 90% confidence.