cluster: fix the bug that region statistics are not updated after flow-round-by-digit change (#4304)

[ti-chi-bot]

This is an automated cherry-pick of #4304

What problem does this PR solve?

fix #4295

What is changed and how it works?

A change in flowRoundDivisor also considers that the flow statistics have changed.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

Fix the bug that region statistics are not updated after `flow-round-by-digit` change.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HunDunDM
• nolouch

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[nolouch]

/merge

[ti-chi-bot]

@nolouch: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ffdc728

[codecov]

Codecov Report

Merging #4305 (384e8a9) into release-5.3 (a2d6504) will decrease coverage by 0.09%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-5.3    #4305      +/-   ##
===============================================
- Coverage        74.96%   74.87%   -0.10%     
===============================================
  Files              264      264              
  Lines            27250    27252       +2     
===============================================
- Hits             20429    20405      -24     
- Misses            5017     5031      +14     
- Partials          1804     1816      +12     

Flag	Coverage Δ
unittests	74.87% <100.00%> (-0.10%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/core/region.go	91.82% <100.00%> (+0.01%)	⬆️
server/core/region_option.go	82.52% <100.00%> (+0.17%)	⬆️
server/grpc_service.go	50.91% <100.00%> (+0.70%)	⬆️
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
server/schedulers/shuffle_hot_region.go	55.55% <0.00%> (-10.11%)	⬇️
pkg/etcdutil/etcdutil.go	82.35% <0.00%> (-5.89%)	⬇️
server/id/id.go	76.19% <0.00%> (-4.77%)	⬇️
server/member/member.go	63.10% <0.00%> (-3.75%)	⬇️
server/schedulers/random_merge.go	60.00% <0.00%> (-3.34%)	⬇️
server/server.go	71.40% <0.00%> (-2.25%)	⬇️
... and 8 more

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