feat(server): add evaluation timing observability

[abhinav-galileo]

Summary:

• Adds timing metrics around evaluation execution stages.
• Adds tracing spans around engine and Luna evaluator paths.
• Adds optional Luna HTTP phase and client timing diagnostics.

Validation:

• git diff --check passed for the split diff.
• make engine-test did not reach tests because uv timed out fetching greenlet from the package index.

[codecov]

Codecov Report

❌ Patch coverage is 86.11111% with 45 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
engine/src/agent_control_engine/core.py	89.81%	11 Missing ⚠️
...rc/agent_control_evaluator_galileo/luna/metrics.py	70.27%	11 Missing ⚠️
...src/agent_control_evaluator_galileo/luna/client.py	88.88%	10 Missing ⚠️
...rc/agent_control_evaluator_galileo/luna/tracing.py	77.41%	7 Missing ⚠️
...r/src/agent_control_server/endpoints/evaluation.py	79.31%	6 Missing ⚠️

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