Fix hex color component parsing

[haaaaaaarshs]

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This PR fixes custom .colorset parsing when asset catalog component values are stored as hexadecimal strings such as "0x94" or "0XFF".

The existing parser attempted to parse every color component with Double(...), which works for normalized decimal strings like "1.000" but fails for hex component strings. This change adds a small parsing path for 0x / 0X values and converts those 8-bit channel values into normalized Double values between 0 and 1, while keeping the existing decimal parsing behavior unchanged.

Closes #146

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• REQUIRED: I have tested my change locally with swift test
• OPTIONAL: I have tested my change on an iOS simulator or device
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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes:

AI was used to review the implementation for correctness and scope before submission. I manually reviewed the code changes, checked that the implementation specifically handles 0x / 0X hex component strings, preserved the existing decimal parsing behavior, and tested the project locally with swift test.

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