op-node: Set RPC timeouts

This is done in BaseClient because all RPC calls in the op-node
flow through the base client. I have set it to 10s for the
CallContext and 20s for the BatchCallContext. These values
are large enough to handle complex computation, but will prevent
a slow loris or throttling attack. Smaller timeouts can stil be
set further up the chain.

op-node/client/rpc.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"regexp"
+	"time"
 
 	"github.com/ethereum-optimism/optimism/op-service/backoff"
 	"github.com/ethereum/go-ethereum"
@@ -62,6 +63,7 @@ func DialRPCClientWithBackoff(ctx context.Context, log log.Logger, addr string,
 
 // BaseRPCClient is a wrapper around a concrete *rpc.Client instance to make it compliant
 // with the client.RPC interface.
+// It sets a timeout of 10s on CallContext & 20s on BatchCallContext made through it.
 type BaseRPCClient struct {
 	c *rpc.Client
 }
@@ -75,11 +77,15 @@ func (b *BaseRPCClient) Close() {
 }
 
 func (b *BaseRPCClient) CallContext(ctx context.Context, result any, method string, args ...any) error {
-	return b.c.CallContext(ctx, result, method, args...)
+	cCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	return b.c.CallContext(cCtx, result, method, args...)
 }
 
 func (b *BaseRPCClient) BatchCallContext(ctx context.Context, batch []rpc.BatchElem) error {
-	return b.c.BatchCallContext(ctx, batch)
+	cCtx, cancel := context.WithTimeout(ctx, 20*time.Second)
+	defer cancel()
+	return b.c.BatchCallContext(cCtx, batch)
 }
 
 func (b *BaseRPCClient) EthSubscribe(ctx context.Context, channel any, args ...any) (ethereum.Subscription, error) {