Add OTEL telemetry for exec sessions

[fkorotkov-oai]

Summary

• initialize OTLP trace and log providers alongside the existing metric provider
• instrument VM exec setup, session, and attachment lifecycles with OTEL spans, lifecycle logs, and operational metrics
• add in-memory SDK unit tests that assert logs, metrics, and traces together without exporting raw command text

Validation

• go test ./internal/controller ./internal/opentelemetry
• go test ./... was attempted locally, but the real Tart VM integration suite timed out in internal/tests after 10 minutes