removed `Channels` class, bug fixes/corrections for `Thread` tests

• uv_queue_work is very buggy, after thread is finished it's work, the callback feature has issues.
  • On Linux causes segmentation faults.
  • On Windows not even called at all.
    • As so, uv_async_send is used instead.
  • The way memory is currently handled by libuv and uv_queue_work passing Channels objects is easily corrupted.
  • Multiple uv_queue_work threads calls need special care, causes segmentation faults.