[Bug]: `declare` statements are not preserved which breaks API extending for 3rd-party modules

Version

  System:
    OS: Linux 6.1 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
    CPU: (2) x64 AMD EPYC
    Memory: 2.74 GB / 4.14 GB
    Container: Yes
    Shell: Unknown
  npmPackages:
    @rslib/core: ^0.5.1 => 0.5.1

Details

Input:

declare global {
  const x: string;
}

declare module "unist" {
  interface Data {
    key: string;
  }
}

export * from "./test";

Output:

export declare const y: string;

export { }

Reproduce link

https://codesandbox.io/p/devbox/thirsty-leftpad-h3fczd

Reproduce Steps

npm run build

Start with the TypeScript input and output shown in the issue, then run the provided CodeSandbox reproduction with npm run build. Compare how the declare global and declare module statements are handled; done means those declarations are preserved while the API extension remains usable.