fix(levm): improve get state transitions LEVM (#2518)

**Motivation**

<!-- Why does this pull request exist? What are its goals? -->
- Make `get_state_transitions` we use un LEVM return the same as the one
in REVM.

**Description**

<!-- A clear and concise general description of the changes this PR
introduces -->
- I made changes in the past to make `get_state_transitions` for both
LEVM and REVM the same for comparison but I missed one aspect. We only
want to show the code in an `AccountUpdate` if the code itself has been
modified, not just the `AccountInfo`. Before we were returning the code
in the `AccountUpdate` even if only the nonce of the contract changed
for example.

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes #issue_number

Author: JereSalo

cmd/ef_tests/blockchain/test_runner.rs

@@ -6,7 +6,7 @@ use crate::{
 };
 use ethrex_blockchain::{fork_choice::apply_fork_choice, Blockchain};
 use ethrex_common::types::{
-    Account as CoreAccount, Block as CoreBlock, BlockHeader as CoreBlockHeader,
+    Account as CoreAccount, Block as CoreBlock, BlockHeader as CoreBlockHeader, EMPTY_KECCACK_HASH,
 };
 use ethrex_rlp::decode::RLPDecode;
 use ethrex_storage::{EngineType, Store};
@@ -177,16 +177,19 @@ async fn check_poststate_against_db(test_key: &str, test: &TestUnit, db: &Store)
         );
         // Check code
         let code_hash = expected_account.info.code_hash;
-        let db_account_code = db
-            .get_account_code(code_hash)
-            .expect("Failed to read from DB")
-            .unwrap_or_else(|| {
-                panic!("Account code for code hash {code_hash} not found in DB test:{test_key}")
-            });
-        assert_eq!(
-            db_account_code, expected_account.code,
-            "Mismatched account code for code hash {code_hash} test:{test_key}"
-        );
+        if code_hash != *EMPTY_KECCACK_HASH {
+            // We don't want to get account code if there's no code.
+            let db_account_code = db
+                .get_account_code(code_hash)
+                .expect("Failed to read from DB")
+                .unwrap_or_else(|| {
+                    panic!("Account code for code hash {code_hash} not found in DB test:{test_key}")
+                });
+            assert_eq!(
+                db_account_code, expected_account.code,
+                "Mismatched account code for code hash {code_hash} test:{test_key}"
+            );
+        }
         // Check storage
         for (key, value) in expected_account.storage {
             let db_storage_value = db

crates/vm/backends/levm/mod.rs

@@ -185,9 +185,12 @@ impl LEVM {
             }
 
             let new_state_code_hash = code_hash(&new_state_account.info.bytecode);
-            if initial_state_account.bytecode_hash() != new_state_code_hash {
+            let code = if initial_state_account.bytecode_hash() != new_state_code_hash {
                 acc_info_updated = true;
-            }
+                Some(new_state_account.info.bytecode.clone())
+            } else {
+                None
+            };
 
             // 2. Storage has been updated if the current value is different from the one before execution.
             let mut added_storage = HashMap::new();
@@ -199,17 +202,14 @@ impl LEVM {
                 }
             }
 
-            let (info, code) = if acc_info_updated {
-                (
-                    Some(AccountInfo {
-                        code_hash: new_state_code_hash,
-                        balance: new_state_account.info.balance,
-                        nonce: new_state_account.info.nonce,
-                    }),
-                    Some(new_state_account.info.bytecode.clone()),
-                )
+            let info = if acc_info_updated {
+                Some(AccountInfo {
+                    code_hash: new_state_code_hash,
+                    balance: new_state_account.info.balance,
+                    nonce: new_state_account.info.nonce,
+                })
             } else {
-                (None, None)
+                None
             };
 
             let mut removed = !initial_state_account.is_empty() && new_state_account.is_empty();