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>

beacon_node/network/src/sync/tests/mod.rs

@@ -11,7 +11,6 @@ use beacon_processor::WorkEvent;
 use lighthouse_network::rpc::RequestType;
 use lighthouse_network::service::api_types::{AppRequestId, Id};
 use lighthouse_network::{NetworkGlobals, PeerId};
-use rand_chacha::ChaCha20Rng;
 use slot_clock::ManualSlotClock;
 use std::collections::{HashMap, HashSet};
 use std::fs::OpenOptions;
@@ -72,9 +71,8 @@ struct TestRig {
     network_globals: Arc<NetworkGlobals<E>>,
     /// Beacon chain harness
     harness: BeaconChainHarness<EphemeralHarnessType<E>>,
-    /// `rng` for generating test blocks and blobs.
     rng_08: rand_chacha_03::ChaCha20Rng,
-    rng: ChaCha20Rng,
+    unstructured: arbitrary::Unstructured<'static>,
     fork_name: ForkName,
     /// Blocks that will be used in the test but may not be known to `harness` yet.
     network_blocks_by_root: HashMap<Hash256, RangeSyncBlock<E>>,