br: fix stats meta count is zero if no checksum 8.5

[Leavrth]

What problem does this PR solve?

Issue Number: close #60978

Problem Summary:
the count of stats_meta is zero if backup has no checksum

What changed and how does it work?

get the count of stats_meta by collecting the files instead of total kvs of table.

Check List

Tests

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

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @Leavrth. Thanks for your PR.

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[codecov]

Codecov Report

❌ Patch coverage is 86.36364% with 3 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5@e89731e). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #63420   +/-   ##
================================================
  Coverage               ?   58.1882%           
================================================
  Files                  ?       1783           
  Lines                  ?     641420           
  Branches               ?          0           
================================================
  Hits                   ?     373231           
  Misses                 ?     243504           
  Partials               ?      24685           

Flag	Coverage Δ
integration	39.2339% <86.3636%> (?)
unit	72.7633% <40.9090%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.1541% <0.0000%> (?)

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-17 10:10:56.330538572 +0000 UTC m=+8217.809119209: ☑️ agreed by BornChanger.
• 2025-09-19 06:56:54.91193944 +0000 UTC m=+169376.390520107: ☑️ agreed by 3pointer.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer, BornChanger, YuJuncen

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[BornChanger]

/retest

[tiprow]

@BornChanger: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

Details

In response to this:

/retest

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #63627.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #63628.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #63629.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #63630.