sinkv2(ticdc): directly advance checkpoint ts if only resolved ts (#7876)

[ti-chi-bot]

This is an automated cherry-pick of #7876

What problem does this PR solve?

Issue Number: close #7887

What is changed and how it works?

• Directly advance checkpoint ts if only resolved ts. If there are no events, we can just advance checkpoint ts.
• Reduce the buffer size from 1024 * 1024 to 4096.

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

Questions

Will it cause performance regression or break compatibility?

No

Do you need to update user documentation, design documentation or monitoring documentation?

No

Release note

Directly advance checkpoint TS to reduce OOM risk if there is no row change events

[ti-chi-bot]

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[Rustin170506]

/merge

[ti-chi-bot]

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

Commit hash: e945b1f

[Rustin170506]

/run-integration-test