fix(stream): reuse label guarded metrics for actor input output metrics

[wenym1]

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What's changed and what's your intention?

Fix #13948

The cause is the same as described in #13966 (comment).

The reason for failing to resolve the issue with #13966 (comment) is that, in d1fedcb, in the metric report of dispatch, we call with_label_values in each dispatch call similar to in other code in the commit. However, the other code is generating long existing streams, but the dispatch is a async method call. So the value returned from with_label_values in dispatch is still dropped immediately, and the problem still exists.

Actually in d1fedcb the problem is half resolved. The actor input metrics is reported correctly already with the fix. In this PR we change to store the value returned from with_label_values as a field in the dispatch executor. The actor output metrics is reported correctly now.

Following in the grafana dashboard, we first run in d1fedcb, the input metrics is fixed while the output metrics is still with problem. Later we run code in this PR, and both the input and output metrics is fixed.

Checklist

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[fuyufjh]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8b2b3f7) 67.99% compared to head (c016836) 67.97%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13994      +/-   ##
==========================================
- Coverage   67.99%   67.97%   -0.03%     
==========================================
  Files        1536     1536              
  Lines      265403   265430      +27     
==========================================
- Hits       180462   180414      -48     
- Misses      84941    85016      +75     

Flag	Coverage Δ
rust	67.97% <100.00%> (-0.03%)	⬇️

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