Test the pruning of excess peers using randomly generated input (#3248)

## Issue Addressed

https://github.com/sigp/lighthouse/issues/3092


## Proposed Changes

Added property-based tests for the pruning implementation. A randomly generated input for the test contains connection direction, subnets, and scores.


## Additional Info

I left some comments on this PR, what I have tried, and [a question](https://github.com/sigp/lighthouse/pull/3248#discussion_r891981969).

Co-authored-by: Diva M <divma@protonmail.com>

beacon_node/lighthouse_network/src/peer_manager/peerdb/score.rs

@@ -223,6 +223,7 @@ impl RealScore {
     #[cfg(test)]
     pub fn set_gossipsub_score(&mut self, score: f64) {
         self.gossipsub_score = score;
+        self.update_state();
     }
 
     /// Applies time-based logic such as decay rates to the score.