Gets the newest block number.
curl --location --request POST '127.0.0.1:1926' \ --header 'Content-Type: application/json' \ --data-raw '{ "jsonrpc": "2.0", "id": 1, "params": {}, "method": "GetBlockCount" }'
{ "id": 1, "result": { "index": 354596 }, "error": null }