Improve activity log throttling check

[SangJunBak]

Updated the throttling_check and statement_logging_throttling_check methods to return bool instead of Option<usize>, simplifying the logic for determining whether a statement should be throttled. Added a new method log_prepared_statement to handle logging of prepared statements and adjusted related logic in get_prepared_statement_info. Enhanced test coverage for statement logging throttling behavior.

Motivation

• This PR fixes a recognized bug.

• https://github.com/MaterializeInc/database-issues/issues/9922
• https://github.com/MaterializeInc/database-issues/issues/9604

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.