fix: spawn options are processed

[jliben]

While using this nice lib to compress a pretty big folder, I realized that the child_process is spawned as a background process.
On my (windows) machine, this leads to the 7za child to continue running when I interrupt the node.js program that spawned it.

I think it would make sense to default the detached option of the child_process to false, however, in order to keep background compatibility, I tried to use the documented $spawnOptions, like so:

      const compressStream = add(
        path.resolve(RELEASE_DIR, "archive.7z"),
        ".",
        {
          $bin: sevenBin.path7za,
          $progress: true,
          $spawnOptions: {
            detached: false,
          },
        }
      )

Just realised it was not processed, so I'm submitting this little fix to support it.

Basic unit tests added as well, I could not really figure out how to write more advanced integration tests.

[jliben]

oops I forgot to remove the only flag here :)