fix(cluster,core): refine DFS stats collection log and filtering

[JmPotato]

What problem does this PR solve?

Issue Number: ref #9707.

What is changed and how does it work?

- Updated store stats collection to skip DFS stat items with zero written bytes and write requests.
- Added logging of collection duration and item count.
- Expanded unit tests to cover filtering of zero-value DFS stat entries and verify aggregation correctness.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[codecov]

Codecov Report

❌ Patch coverage is 68.18182% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.79%. Comparing base (e30504e) to head (44d3114).
⚠️ Report is 2 commits behind head on master.

❌ Your patch status has failed because the patch coverage (68.18%) is below the target coverage (74.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9792      +/-   ##
==========================================
+ Coverage   76.76%   76.79%   +0.03%     
==========================================
  Files         491      491              
  Lines       78466    78480      +14     
==========================================
+ Hits        60231    60266      +35     
+ Misses      14559    14537      -22     
- Partials     3676     3677       +1     

Flag	Coverage Δ
unittests	76.79% <68.18%> (+0.03%)	⬆️

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ti-chi-bot]

@JmPotato: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
non-block/pull-unit-test-next-gen	44d3114	link	false	/test pull-unit-test-next-gen

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: okJiang, rleungx

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [rleungx]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-30 02:35:25.556130077 +0000 UTC m=+138505.812861477: ☑️ agreed by okJiang.
• 2025-09-30 03:41:52.896358453 +0000 UTC m=+142493.153089873: ☑️ agreed by rleungx.