Small refactor and additional test coverage for server audit plugin

[tonychen2001]

Description

Minor code simplification and additional test coverage in the server audit plugin.

1. Simplify event filtering logic

• Replace if-else chain with a single bitwise AND check for query event type filtering (DDL/DML/DCL)
• Remove goto statements and unused orig_query variable

2. Add test coverage for SQL including comments (related to 635559a)

• Add MTR tests validating that queries with various comment styles are properly logged:
  • -- comment, # comment, /*! ... */, /*M! ... */
  • Version-specific comments (/*!100100 ... */, /*M!100100 ... */)
  • Control characters in comments
• These tests validate the fix from commit 635559a which removed the custom SQL parser

3. Expand password obfuscation test coverage

• Add test cases verifying passwords are masked (*****) in audit logs for:
  • GRANT ... IDENTIFIED BY
  • CHANGE MASTER ... MASTER_PASSWORD
  • CREATE SERVER ... PASSWORD
  • ALTER SERVER ... PASSWORD

Release Notes

N/A

How can this PR be tested?

Additional test cases were added to the server_audit MTR.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.

Copyright

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

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✅ tonychen2001
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