fix(core): GethTrace shouldn't have 0x prefix for return_value (#1705)

ethers-core/src/types/trace/geth.rs

@@ -1,13 +1,13 @@
 use crate::types::{Bytes, H256, U256};
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize, Serializer};
 use std::collections::BTreeMap;
 
 // https://github.com/ethereum/go-ethereum/blob/a9ef135e2dd53682d106c6a2aede9187026cc1de/eth/tracers/logger/logger.go#L406-L411
 #[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
 pub struct GethTrace {
     pub failed: bool,
     pub gas: u64,
-    #[serde(rename = "returnValue")]
+    #[serde(serialize_with = "serialize_bytes", rename = "returnValue")]
     pub return_value: Bytes,
     #[serde(rename = "structLogs")]
     pub struct_logs: Vec<StructLog>,
@@ -54,3 +54,11 @@ pub struct GethDebugTracingOptions {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub timeout: Option<String>,
 }
+
+fn serialize_bytes<S, T>(x: T, s: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+    T: AsRef<[u8]>,
+{
+    s.serialize_str(&hex::encode(x.as_ref()))
+}