[#3860] Optimize gray routing rule algorithm

[chengyouling]

No description provided.

[liubao68]

re-run ci

[liubao68]

re-run ci

[codecov-commenter]

Codecov Report

Merging #3861 (028154d) into 2.8.x (6712e96) will increase coverage by 0.01%.
The diff coverage is 60.00%.

❗ Current head 028154d differs from pull request most recent head 272eb26. Consider uploading reports for the commit 272eb26 to get more accurate results

@@             Coverage Diff              @@
##              2.8.x    #3861      +/-   ##
============================================
+ Coverage     74.42%   74.43%   +0.01%     
  Complexity      690      690              
============================================
  Files          1592     1592              
  Lines         40013    39987      -26     
  Branches       3654     3647       -7     
============================================
- Hits          29778    29766      -12     
+ Misses         8743     8732      -11     
+ Partials       1492     1489       -3     

Impacted Files	Coverage Δ
...b/router/distribute/AbstractRouterDistributor.java	84.09% <55.55%> (+14.86%)	⬆️
...pache/servicecomb/router/model/PolicyRuleItem.java	71.42% <100.00%> (+8.92%)	⬆️

... and 9 files with indirect coverage changes

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