Feature: Support case-insensitive enum resolution

[PeyaPeyaPeyang]

Hi mainteners,

Currently, EnumArgumentResolver resolves enums in a case-sensitive manner.
For example, MyEnum.VALUE cannot be resolved from "value" or "Value".

It would be useful to allow optional case-insensitive resolution, for example via a flag or annotation:

@Execute
public void test(@Arg("test") @CaseInsensitive MyEnum value) {
    // Resolves "value", "VALUE", or any case variation
}

This makes enum arguments easier to use and commands more user-friendly.
For example, if a command takes a platform-specific GameMode enum as an argument, using this annotation lets "creative" work instead of "CREATIVE", which is much more convenient.

Thanks.