🧪 test: add unit tests for dataUrlToBytes

[MarsLuay]

🧪 What: Added unit test coverage for dataUrlToBytes function in src/renderedPdfExport.ts.
📊 Coverage: Covered standard data URLs with headers, custom MIME types, raw base64 strings without commas, empty string and payload edge cases, and 8-bit byte range binary conversions (0x00 to 0xFF).
✨ Result: Increased unit test coverage and reliability for string to byte array conversion during rendered PDF export.

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PR created automatically by Jules for task 12149703863362323380 started by @MarsLuay

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