cluster tests (#101)

* Add cluster tests

This tests behaviors in cluster environments.

* Skip cluster tests in CI

The suite of cluster tests requires a significant number of redis instances, which I'm going to avoid creating in GH actions right now.

* add note about hash slots

* improve docs further, fix compose dependencies

* use docker compose for tests in CI

* use docker compose for all CI commands

* add 5s sleep before testing

We tend to get test errors due to unready redis clusters when they are spun up alongside the runner service. This adds a delay as a hack around this.

* move sleep to be ci-specific

* upgrade deps

* Revert "move sleep to be ci-specific"

This reverts commit 290da8baca1f7f1a0f499dd019bbbf421cd23ace.

* use only 3 seconds sleep

* add cluster readiness checks to the tests directly