Migrate to Lumos v0.21

Deprecated the httpAgent and httpsAgent in RPC.setNode

Please use the fetch option in RPC constructor instead.

-const rpc = new RPC(url)
+const rpc = new RPC(
+ url,
+ { fetch: (request, init) => originalFetch(request, { ...init, keepalive: true }) },
+)
-rpc.setNode({ url, httpAgent, httpsAgent })
+rpc.setNode({ url })