Postman Generator: Format json edge case

[gcatanese]

Address edge case (JSON formatting) - cubic-dev comment

@wing328

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Summary by cubic

Ensures tag names and descriptions in the postman-collection generator are properly JSON-escaped, including control characters, to prevent invalid Postman JSON and broken imports.

• Bug Fixes
  • Escape control characters in tag names/descriptions using JsonStringEncoder in PostmanCollectionCodegen.
  • Added test and sample spec to verify escaping for \t, \b, \f, \r, and \n.

^{Written for commit 7f0ba9c. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files