set timestamp to null if it was set to 0 (#14)

## 📝 Summary

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## ⛱ Motivation and Context

<!--- Why is this change required? What problem does it solve? -->

## 📚 References

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---

## ✅ I have run these commands

* [ ] `make lint`
* [ ] `make test`
* [ ] `go mod tidy`

proxy/sender_proxy.go

@@ -122,6 +122,14 @@ func (prx *SenderProxy) EthSendBundle(ctx context.Context, ethSendBundle rpctype
 		return err
 	}
 
+	// quick workaround for people setting timestamp to 0
+	if ethSendBundle.MaxTimestamp != nil && *ethSendBundle.MaxTimestamp == 0 {
+		ethSendBundle.MaxTimestamp = nil
+	}
+	if ethSendBundle.MinTimestamp != nil && *ethSendBundle.MinTimestamp == 0 {
+		ethSendBundle.MinTimestamp = nil
+	}
+
 	return prx.HandleParsedRequest(ctx, parsedRequest)
 }