statistics: rename subscriber and handle drop schema event

[0xPoe]

What problem does this PR solve?

Issue Number: ref #57871

Problem Summary:

What changed and how does it work?

Split from #57872

1. Renamed the handler to "subscriber" to avoid conflict with an existing handler in this package.
2. Correctly handled the schema drop event.

This will be integrated into my next PR, so additional tests will be added. We plan to update the tests in subsequent PRs.

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

[0xPoe]

🔢 Self-check (PR reviewed by myself and ready for feedback.)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 73.8467%. Comparing base (30069c5) to head (baebd82).
Report is 121 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58009        +/-   ##
================================================
+ Coverage   73.1633%   73.8467%   +0.6833%     
================================================
  Files          1674       1704        +30     
  Lines        461261     469345      +8084     
================================================
+ Hits         337474     346596      +9122     
+ Misses       103041     101276      -1765     
- Partials      20746      21473       +727     

Flag	Coverage Δ
integration	46.0784% <0.0000%> (?)
unit	72.3186% <0.0000%> (+0.0289%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	45.9743% <ø> (-0.0331%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, qw4990

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-12-05 08:22:07.493605997 +0000 UTC m=+1315915.113260510: ☑️ agreed by lance6716.
• 2024-12-05 08:26:10.968142384 +0000 UTC m=+1316158.587796899: ☑️ agreed by qw4990.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #58457.