feat: add timer metrics

[hwjiangkai]

What problem does this PR solve?

add timer metrics

Issue Number: close #xxx

Problem Summary

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

[codecov]

Codecov Report

Merging #254 (5abca24) into main (ca600ab) will decrease coverage by 0.00%.
The diff coverage is 63.63%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #254      +/-   ##
==========================================
- Coverage   64.00%   63.99%   -0.01%     
==========================================
  Files         129      129              
  Lines       11575    11585      +10     
==========================================
+ Hits         7408     7414       +6     
- Misses       3643     3647       +4     
  Partials      524      524              

Impacted Files	Coverage Δ
internal/timer/timingwheel/timingwheel.go	79.31% <63.63%> (-0.39%)	⬇️
internal/gateway/gateway.go	69.60% <0.00%> (-0.30%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca600ab...5abca24. Read the comment docs.

[wenfengwang]

LGTM