add rstest_reuse

[conorbros]

Small helper library that removes duplications from our rstest setup for the Cassandra integration tests.

[github-actions]

0 benchmark regressed. 2 benchmark improved. Please check the benchmark workflow logs for full details: https://github.com/shotover/shotover-proxy/actions/runs/6258635367

  1 (1.00%) low mild
  4 (4.00%) high mild
  1 (1.00%) high severe
transform/redis_cluster_ports_rewrite
                        time:   [1.0573 µs 1.0716 µs 1.0860 µs]
                        change: [-34.521% -28.149% -24.130%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  4 (4.00%) high mild
transform/cassandra_request_throttling_unparsed
                        time:   [774.97 ns 784.02 ns 795.11 ns]
                        change: [-24.654% -23.498% -22.189%] (p = 0.00 < 0.05)
                        Performance has improved.

[rukai]

seems reasonable