feat(tracing): adding eth client tracing (#2960)

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## Overview

This PR follows the same pattern as the previous PR and creates a
decorator around the eth client that injects tracing.

Sample grafana output with metrics enabled.

<img width="912" height="741" alt="image"
src="https://github.com/user-attachments/assets/9d32f48e-a01c-47c7-94a3-168d44aa5fe9"
/>

<img width="902" height="542" alt="image"
src="https://github.com/user-attachments/assets/a777a28e-5f3b-42e0-a31a-7527521c249b"
/>



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Author: chatton

execution/evm/eth_rpc_client.go

@@ -0,0 +1,30 @@
+package evm
+
+import (
+	"context"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/ethclient"
+)
+
+type ethRPCClient struct {
+	client *ethclient.Client
+}
+
+func NewEthRPCClient(client *ethclient.Client) EthRPCClient {
+	return &ethRPCClient{client: client}
+}
+
+func (e *ethRPCClient) HeaderByNumber(ctx context.Context, number *big.Int) (*types.Header, error) {
+	return e.client.HeaderByNumber(ctx, number)
+}
+
+func (e *ethRPCClient) GetTxs(ctx context.Context) ([]string, error) {
+	var result []string
+	err := e.client.Client().CallContext(ctx, &result, "txpoolExt_getTxs")
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}

execution/evm/eth_rpc_tracing.go

@@ -0,0 +1,82 @@
+package evm
+
+import (
+	"context"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/core/types"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+	"go.opentelemetry.io/otel/trace"
+)
+
+// tracedEthRPCClient wraps an EthRPCClient and records spans for observability.
+type tracedEthRPCClient struct {
+	inner  EthRPCClient
+	tracer trace.Tracer
+}
+
+// withTracingEthRPCClient decorates an EthRPCClient with OpenTelemetry tracing.
+func withTracingEthRPCClient(inner EthRPCClient) EthRPCClient {
+	return &tracedEthRPCClient{
+		inner:  inner,
+		tracer: otel.Tracer("ev-node/execution/eth-rpc"),
+	}
+}
+
+func (t *tracedEthRPCClient) HeaderByNumber(ctx context.Context, number *big.Int) (*types.Header, error) {
+	var blockNumber string
+	if number == nil {
+		blockNumber = "latest"
+	} else {
+		blockNumber = number.String()
+	}
+
+	ctx, span := t.tracer.Start(ctx, "Eth.GetBlockByNumber",
+		trace.WithAttributes(
+			attribute.String("method", "eth_getBlockByNumber"),
+			attribute.String("block_number", blockNumber),
+		),
+	)
+	defer span.End()
+
+	result, err := t.inner.HeaderByNumber(ctx, number)
+	if err != nil {
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+		return nil, err
+	}
+
+	span.SetAttributes(
+		attribute.String("block_hash", result.Hash().Hex()),
+		attribute.String("state_root", result.Root.Hex()),
+		attribute.Int64("gas_limit", int64(result.GasLimit)),
+		attribute.Int64("gas_used", int64(result.GasUsed)),
+		attribute.Int64("timestamp", int64(result.Time)),
+	)
+
+	return result, nil
+}
+
+func (t *tracedEthRPCClient) GetTxs(ctx context.Context) ([]string, error) {
+	ctx, span := t.tracer.Start(ctx, "TxPool.GetTxs",
+		trace.WithAttributes(
+			attribute.String("method", "txpoolExt_getTxs"),
+		),
+	)
+	defer span.End()
+
+	result, err := t.inner.GetTxs(ctx)
+	if err != nil {
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+		return nil, err
+	}
+
+	span.SetAttributes(
+		attribute.Int("tx_count", len(result)),
+	)
+
+	return result, nil
+}