fix(ratelimiter): log metrics server failure instead of swallowing it

[mesutoezdil]

setupMetrics swallowed the ListenAndServe error in an empty branch, so a
failed Prometheus bind left the service running with no metrics and no log
line. Now logs at error level, matching setupPprof and setupOlricStats.

Issues

Closes #540

Summary by CodeRabbit

• Bug Fixes
  • Added error logging when the rate-limiter metrics service fails to start, improving visibility into service startup issues.

[coderabbitai]

📝 Walkthrough

Walkthrough

The rate-limiter metrics HTTP listener now logs errors returned by ListenAndServe, including failures to start the /metrics server.

Changes

Rate-limiter metrics

Layer / File(s)	Summary
Log metrics listener failures src/invocation-plane-services/ratelimiter/cmd/main.go	Records ListenAndServe failures with an error-level zap log.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Suggested reviewers: balajinvda

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The change logs the metrics listener failure, satisfying issue #540 and preventing the error from being silently discarded.
Out of Scope Changes check	✅ Passed	The single-line change is limited to the linked issue objective and contains no unrelated modifications.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title follows Conventional Commits and accurately identifies the ratelimiter bug fix.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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