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