specta_typescript doesn't respect #[serde(flatten)] inside enum variants

[Vlad-Shcherbina]

To reproduce, run the following program:

[dependencies]
# latest trunk
specta = { git = "https://github.com/specta-rs/specta", rev = "ff4ba3a908cfe7552692aab50d74cdd487cae57f", features = ["derive"] }
specta-typescript = { git = "https://github.com/specta-rs/specta", rev = "ff4ba3a908cfe7552692aab50d74cdd487cae57f" }

serde = { version = "1.0.216", features = ["derive"] }
serde_json = "1.0.133"

use specta::Type as _;

#[derive(serde::Serialize, specta::Type)]
enum MyEnum {
    Variant {
        #[serde(flatten)]
        inner: MyInnerStruct,
    },
}

#[derive(serde::Serialize, specta::Type)]
struct MyInnerStruct {
    some_field: i32,
}

fn main() {
    let mut types = specta::TypeCollection::default();
    MyEnum::definition(&mut types);

    let s = specta_typescript::Typescript::default().export(&types).unwrap();
    println!("{s}");
    println!("------");
    let s = serde_json::to_string_pretty(&MyEnum::Variant { inner: MyInnerStruct { some_field: 42 } }).unwrap();
    println!("{s}");
}

This outputs:

// This file has been generated by Specta. DO NOT EDIT.

export type MyEnum = { Variant: { inner: MyInnerStruct } };

export type MyInnerStruct = { some_field: number };
------
{
  "Variant": {
    "some_field": 42
  }
}

Instead it should be something like

export type MyEnum = { Variant: { some_field: number } };