ddl: close lightning writers after the import is complete (#39879)

[ti-chi-bot]

This is an automated cherry-pick of #39879

What problem does this PR solve?

Issue Number: close #39800

Problem Summary:

When the import is completed, the memory allocated by the lightning writers is not explicitly released. This is fine in normal cases, but when CGO is used to allocate the memory, the leakage happened.

What is changed and how it works?

As the title said.

Check List

Tests

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

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

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Benjamin2037
• hawkingrei

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[Benjamin2037]

LGTM

[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: fc5a039