[Rust] add enum for fury macro derive

[peacess]

as title

[theweipeng]

Hi, could you please clarify if you intend to add an enum to the macro, or if you're suggesting that the macro should be modified to support enums? Additional details would be helpful as the request is a bit ambiguous. Thanks!

[jiacai2050]

fury/rust/fury-derive/src/object/serializer.rs

Lines 25 to 29 in e99b46f

	let fields = match &ast.data {
	syn::Data::Struct(s) => sorted_fields(&s.fields),
	_ => {
	panic!("only struct be supported")
	}

It seems this is where we need to fix, please assign this issue to me. @theweipeng

[jiacai2050]

This spec says enum are serialized as unsigned var int, but in Rust enum could carry payload, such as:

enum Location {
    Unknown,
    Anonymous,
    Known(Coord),
}

enum ComplexEnum {
    Nothing,
    Something(u32),
    LotsOfThings {
        usual_struct_stuff: bool,
        blah: String,
    }
}

Those are actually tagged unions, so in first version I will only support enum without any payload, and we may need to discuss how to serialize those union.

@theweipeng @chaokunyang

[jiacai2050]

https://serde.rs/enum-representations.html

Serde has 4 methods to serialize enum.