Use build_result_gas helper in system call gas handling

Replace manual ResultGas construction with the shared build_result_gas
function for consistency with the main execution path.

Author: rakita

crates/handler/src/handler.rs

@@ -1,6 +1,7 @@
 use crate::{
     evm::FrameTr,
-    execution, post_execution,
+    execution,
+    post_execution::{self, build_result_gas},
     pre_execution::{self, apply_eip7702_auth_list},
     validation, EvmTr, FrameResult, ItemOrResult,
 };
@@ -132,10 +133,7 @@ pub trait Handler {
             .and_then(|exec_result| {
                 // System calls have no intrinsic gas; build ResultGas from frame result.
                 let gas = exec_result.gas();
-                let result_gas = ResultGas::default()
-                    .with_total_gas_spent(gas.total_gas_spent())
-                    .with_refunded(gas.refunded() as u64)
-                    .with_state_gas_spent(gas.state_gas_spent());
+                let result_gas = build_result_gas(&gas, init_and_floor_gas);
                 self.execution_result(evm, exec_result, result_gas)
             }) {
             out @ Ok(_) => out,