fix(jira): pass through array-type checklist fields unchanged

[sooperset]

Summary

• Array-type checklist fields (Server/DC Okapya plugin) are now passed through unchanged instead of being converted to markdown strings
• String-type checklist fields (Cloud) continue to use markdown conversion as before
• Added 4 parametrized tests for array-type passthrough behavior

Closes #972

Test plan

• 4 new parametrized tests for array-type checklist passthrough
• Existing 5 Cloud checklist tests still pass (regression)
• Full unit test suite passes (1979 passed)
• pre-commit (ruff + mypy) clean