executor: prevent SELECT AS OF TIMESTAMP with autocommit = 0

[Angel98518]

What problem does this PR solve?

Issue Number: close #65957

According to the description in Stale Read Product Design, SELECT ... AS OF TIMESTAMP should only be used in implicit transactions with autocommit = 1. However, we can still successfully execute the SELECT ... AS OF TIMESTAMP statement even with autocommit = 0.

What changed and how does it work?

This PR adds validation to prevent SELECT ... AS OF TIMESTAMP from being used when autocommit = 0. The validation:

1. Recursively checks if any table in the SELECT statement has an AS OF clause
2. Checks if autocommit is disabled (autocommit = 0)
3. Returns an appropriate error message if both conditions are true

Changes:

• Add hasAsOfClauseInResultSet() helper to recursively check for AS OF clauses in ResultSetNode
• Add hasAsOfClauseInSetOpr() helper to check set operations (UNION, etc.)
• Add validation in ResetContextOfStmt() for both SelectStmt and SetOprStmt
• Return ErrWrongUsage when AS OF TIMESTAMP is used with autocommit = 0

Check List

Tests

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

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

Prevent `SELECT ... AS OF TIMESTAMP` from being used when autocommit = 0, as it should only be used in implicit transactions with autocommit = 1.

---

Contribution by Gittensor, see my contribution statistics at https://gittensor.io/miners/details?githubId=Angel98518

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[Angel98518]

/ok-to-test

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[lance6716]

#65960

This PR is earlier, please wait for it.