Use radom coinbase address for simualations (#291)

## 📝 Summary

This PR makes top of the block simulations use random coinbase address
to make top of the block simulations harder to bypass.

## 💡 Motivation and Context

<!--- (Optional) Why is this change required? What problem does it
solve? Remove this section if not applicable. -->

---

## ✅ I have completed the following steps:

* [ ] Run `make lint`
* [ ] Run `make test`
* [ ] Added tests (if applicable)

crates/rbuilder/src/live_builder/simulation/mod.rs

@@ -8,7 +8,7 @@ use crate::{
     },
     live_builder::order_input::orderpool::OrdersForBlock,
     primitives::{OrderId, SimulatedOrder},
-    utils::gen_uid,
+    utils::{gen_uid, Signer},
 };
 use ahash::HashMap;
 use parking_lot::Mutex;
@@ -107,6 +107,15 @@ where
     ) -> SlotOrderSimResults {
         let (slot_sim_results_sender, slot_sim_results_receiver) = mpsc::channel(10_000);
 
+        let ctx = {
+            // use random coinbase for simulations to make top of the block simulation bypass harder
+            let mut ctx = ctx;
+            let signer = Signer::random();
+            ctx.block_env.coinbase = signer.address;
+            ctx.builder_signer = Some(signer);
+            ctx
+        };
+
         let provider = self.provider.clone();
         let current_contexts = Arc::clone(&self.current_contexts);
         let block_context: BlockContextId = gen_uid();