`svelte-package` doesn't include source maps

Describe the bug

when running svelte-package, it does not include source maps even when they are enabled in svelte.config.js

Reproduction

// svelte.config.js
import preprocess from 'svelte-preprocess';

const config = {
  compilerOptions: {
    enableSourcemap: true,
  },
  preprocess: preprocess({
    sourceMap: true,
  }),
};

export default config;

Logs

No response

System Info

System:
    OS: Windows 10 10.0.19044
    CPU: (12) x64 11th Gen Intel(R) Core(TM) i5-11500T @ 1.50GHz
    Memory: 672.74 MB / 15.73 GB
  Binaries:
    Node: 18.10.0 - C:\Program Files\nodejs\node.EXE
    npm: 8.19.2 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.19041.1266.0), Chromium (105.0.1343.33)
    Internet Explorer: 11.0.19041.1566

Severity

annoyance

Additional Information

the src and the package created by svelte-package:

Start at the svelte-package command and trace how the svelte.config.js settings compilerOptions.enableSourcemap and preprocess sourceMap are handled. Reproduce the package build with the supplied configuration, then verify that the generated package contains the expected source maps.