feat: allow overriding decoration

[a-wallen]

Thanks for the package @rydmike :)

I'd like to have an API for decoration on the ColorCodeField.

My solution preserves your decoration and allows the decoration argument to override it.

There's other solutions as well... like:

1. pass the decoration argument directly to the underlying text field.
2. allow overriding specific properties like borders.

As the maintainer, you to make the call on how you'd like it to be implemented. Let me know haha

Can follow up with a commit to test these changes if you'd like 👍