Use `redis.UniversalClient` instead of `*redis.Client`

[AH-dark]

This enables support for multiple types of redis clients.

UniversalClient is a wrapper client which, based on the provided options, represents either a ClusterClient, a FailoverClient, or a single-node Client. This can be useful for testing cluster-specific applications locally or having different clients in different environments.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (68982eb) 84.97% compared to head (42ba39e) 84.74%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #88 +/- ## =========================================== - Coverage 84.97% 84.74% -0.24% =========================================== Files 17 17 Lines 1278 1278 =========================================== - Hits 1086 1083 -3 - Misses 160 162 +2 - Partials 32 33 +1 ```

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