Add state_root_time_us field to MeterBundleResponse (#148)

The builder returns state_root_time_us in its response but tips was
silently dropping this field during deserialization. Add the field
with serde(default) for backwards compatibility.

Author: niran

crates/core/src/test_utils.rs

@@ -75,5 +75,6 @@ pub fn create_test_meter_bundle_response() -> MeterBundleResponse {
         state_flashblock_index: None,
         total_gas_used: 0,
         total_execution_time_us: 0,
+        state_root_time_us: 0,
     }
 }

crates/core/src/types.rs

@@ -298,6 +298,8 @@ pub struct MeterBundleResponse {
     pub state_flashblock_index: Option<u64>,
     pub total_gas_used: u64,
     pub total_execution_time_us: u128,
+    #[serde(default)]
+    pub state_root_time_us: u128,
 }
 
 #[cfg(test)]