Remove TestRandom (#9006)

We  have a legacy `TestRandom` trait which generates random types for testing and fuzzing.
This function overlaps with `arbitrary` which is used very commonly in the ecosystem.


  Remove `TestRandom` and generate random type instances using `Arbitrary`.


Co-Authored-By: Mac L <mjladson@pm.me>

Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

validator_client/doppelganger_service/Cargo.toml

@@ -19,5 +19,7 @@ types = { workspace = true }
 validator_store = { workspace = true }
 
 [dev-dependencies]
+arbitrary = { workspace = true }
 futures = { workspace = true }
 logging = { workspace = true }
+types = { workspace = true, features = ["arbitrary"] }

validator_client/doppelganger_service/src/lib.rs

@@ -598,14 +598,12 @@ impl DoppelgangerService {
 #[cfg(test)]
 mod test {
     use super::*;
+    use arbitrary::Arbitrary;
     use futures::executor::block_on;
     use slot_clock::TestingSlotClock;
     use std::future;
     use std::time::Duration;
-    use types::{
-        MainnetEthSpec,
-        test_utils::{SeedableRng, TestRandom, XorShiftRng},
-    };
+    use types::MainnetEthSpec;
     use validator_store::DoppelgangerStatus;
 
     const DEFAULT_VALIDATORS: usize = 8;
@@ -641,12 +639,12 @@ mod test {
 
     impl TestBuilder {
         fn build(self) -> TestScenario {
-            let mut rng = XorShiftRng::from_seed([42; 16]);
+            let mut u = types::test_utils::test_unstructured();
             let slot_clock = TestingSlotClock::new(Slot::new(0), GENESIS_TIME, SLOT_DURATION);
 
             TestScenario {
                 validators: (0..self.validator_count)
-                    .map(|_| PublicKeyBytes::random_for_test(&mut rng))
+                    .map(|_| PublicKeyBytes::arbitrary(&mut u).unwrap())
                     .collect(),
                 doppelganger: DoppelgangerService::default(),
                 slot_clock,