Drop dependency on future

Merge requested originally opened at https://github.com/torproject/onionbalance/pull/50

requested review from @rhatto

assigned to @rhatto

I have run both unit and functional tests for this change (along with !5 (merged)) for both Python 3.12.0 and 3.11.2, and they're passing :)

approved this merge request

mentioned in commit 1a9a451e

merged

mentioned in merge request !5 (merged)