Statement level query tag in NodeJS connector

[jiabin-hu]

Summary

• Adds queryTags option to ExecuteStatementOptions for per-statement query tagging
• Implements serializeQueryTags() utility that converts a key/value dict to a comma-separated key:value string (matching the Python connector's format), with backslash-escaping for special characters in values
• Serialized tags are passed via confOverlay["query_tags"] on TExecuteStatementReq, consistent with the Python connector
  implementation

This PR replaces #339

Test plan

• Unit tests for serializeQueryTags covering null/empty input, basic serialization, null values, and special character escaping (tests/unit/utils/queryTags.test.ts)
• Unit tests for executeStatement verifying confOverlay.query_tags is set/unset correctly (tests/unit/DBSQLSession.test.ts)
• Run npm test to confirm all unit tests pass

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[github-actions]

Thanks for your contribution! To satisfy the DCO policy in our contributing guide every commit message must include a sign-off message. One or more of your commits is missing this message. You can reword previous commit messages with an interactive rebase (git rebase -i main).