enhancements to color structure and serialization for echarts option

[devcrocod]

Update the color component structure in the Echarts option to introduce additional features and improve compatibility with different color representations. The proposed changes include:

1. Add support for Hex, Text, Rgb, and Rgba color formats to provide more flexible color specification options
2. Revamp the GradientColors structure to enhance its functionality and make it more intuitive to use
3. Implement dedicated serializers to streamline color serialization and deserialization processes
4. Add test cases to ensure the robustness and reliability of the updated color functionality