txn: use u64::MAX as txn_size for Flush commands

[ekexium]

What is changed and how it works?

Issue Number: Close #16810

What's Changed:

fix: use u64::MAX as txn_size for Flush commands to avoid unexpected resolve_lock_lite

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  • as described in Pipelined-DML uses resolve_lock_lite instead of resolve_lock when there is conflict #16810 , with this PR it is all resolve_locks, though it's still too slow for huge transactions.
• No code

Side effects

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

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• cfzjywxk
• you06

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[cfzjywxk]

LGTM

[ekexium]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 9b0c9b9

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #16900.