test(frontend): cover WorkflowUtilService untested helpers

[Ma77Ball]

What changes were proposed in this PR?

• Add unit tests for updateOperatorVersion covering port rebuild, port preservation, and the unknown-type error.
• Add unit tests for the static parseWorkflowInfo string parsing and object passthrough, and for getNewCommentBox default position and unique ids.

Any related issues, documentation, discussions?

Closes: #6688

How was this PR tested?

• Run: cd frontend && node --max-old-space-size=8192 ./node_modules/nx/dist/bin/nx.js test gui --watch=false --include=src/app/workspace/service/workflow-graph/util/workflow-util.service.spec.ts, expect the suite passing.
• Test-only change; no production code is modified.

Was this PR authored or co-authored using generative AI tooling?

Co-authored with Claude Opus 4.8 in compliance with ASF

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @aglinxinyuan
  You can notify them by mentioning @aglinxinyuan in a comment.

[Copilot]

Pull request overview

Adds missing frontend unit test coverage for WorkflowUtilService helper methods, improving confidence in workflow graph utility behavior without changing production code.

Changes:

• Add unit tests for updateOperatorVersion covering port regeneration, port preservation, and unknown-operator error handling.
• Add unit tests for WorkflowUtilService.parseWorkflowInfo for JSON string parsing vs. object passthrough.
• Add unit tests for getNewCommentBox default position and unique ID generation.

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