fix: allow to use ReadonlyDate in ConfigType

[jakubhonisek]

Summary

This pull request introduces support for the ReadonlyDate type as a valid input for the dayjs() function. The ReadonlyDate type excludes all setter methods from the native Date object, ensuring immutability.

The aim is to allow dates that are typed as ReadonlyDate in projects to be directly passed to the dayjs() function without compatibility issues.

Benefits

• Compatibility with Immutable Dates: Developers can now use ReadonlyDate objects (which exclude setter methods for immutability) as input to the dayjs() function, ensuring smooth integration with projects that require or enforce readonly types.

Impact

• No Breaking Changes: Existing code using Date and other types as input to dayjs() will continue to work as expected.
• Enhanced Flexibility: This change allows developers who use ReadonlyDate in their projects to seamlessly integrate dayjs() without needing to cast or modify their date types.

[martynasoroka]

Nice job Kuba! I really need this change for my personal project, I hope it will be released soon 😄