🧪 [Testing Improvement] Add edge case tests for hexToRgba fallbacks

[BTawaifi]

🎯 What: The testing gap for the hexToRgba function in src/utils.mjs was addressed. The function uses || 0 fallbacks when parsing invalid or partial hex parts, but these edge cases were completely untested.
📊 Coverage: The tests now cover:

• Invalid hex characters causing NaN (e.g., #zzzzzz).
• Short and incomplete hex strings where string slicing returns empty or partial results (e.g., #f, #ff0).
• Missing or malformed inputs like null, undefined, "", and missing # prefix, validating the initial type and format checks return the default values.
  ✨ Result: The test coverage for hexToRgba is now significantly improved, ensuring future refactoring won't accidentally break its error-handling and fallback logic.

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PR created automatically by Jules for task 9579292444359741441 started by @BTawaifi

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