feat: generate enum default as newtype

[Millione]

Motivation

Previously, thrift/protobuf enum type is generated to rust enum type by default, and we provided an annotation pilota.enum_mode="new_type" for users to change the rust generated type to a wrapper of i32. Over time, we found that it is more correct to make the newtype the default behaviour, as when users add a new variant in the enum definition, it will not cause the old idl generated code to fail to decode.

Solution

Deprecate annotation pilota.enum_mode="new_type" and make it as default behaviour.

enum Index {
    A = 0x01,
    B = 0x10,
}

Generated:

pub struct Index(i32);

impl Index {
    pub const A: Self = Self(1);
    pub const B: Self = Self(16);

    pub fn inner(&self) -> i32 {
        self.0
    }
}

impl ::std::convert::From<i32> for Index {
    fn from(value: i32) -> Self {
        Self(value)
    }
}