add debug logging for healthcheck and setup flows in coglet (#2828)
* add debug logging for healthcheck and setup flows in coglet
Add tracing::debug! calls throughout the healthcheck and setup code
paths to improve observability when debugging with RUST_LOG=debug or
COG_LOG_LEVEL=debug.
Healthcheck: log the full request lifecycle from HTTP handler through
service layer, orchestrator handle, event loop dispatch/coalescing,
worker handler invocation, and result distribution.
Setup: log orchestrator config, setup duration, timeout behavior,
health state transitions, setup result status, and setup log drain
sizes across orchestrator, worker, and Python entry point.
* demote healthcheck hot-path logging from debug to trace
The healthcheck endpoint is polled every few seconds by K8s probes.
Keep the happy-path lines at trace to avoid flooding debug logs, while
leaving the unhealthy/error/timeout paths and all setup lines at debug
where they are useful for diagnosing real issues.
