Add bundle-script API

[chr15m]

WIP: when I add bundleScript to the api and run nbb it throws the following error, which is where I'm currently stuck:

$ npx nbb testing.cljs 
node:fs:446
      path = pathModule.toNamespacedPath(getValidatedPath(path));
                                         ^

TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of Buffer or URL. Received null
    at Module.readFileSync (node:fs:446:42)
    at $APP.NAa (file:///home/chrism/dev/nbb/lib/nbb_bundler.js:14:109)
    at file:///home/chrism/dev/nbb/lib/nbb_bundler.js:18:233
    at ModuleJob.run (node:internal/modules/esm/module_job:234:25)
    at async ModuleLoader.import (node:internal/modules/esm/loader:473:24)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:123:5) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Node.js v20.17.0

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