add mainnet

Author: soaryong-stamper

suikotlin/src/main/java/io/cosmostation/suikotlin/model/Network.kt

@@ -1,6 +1,8 @@
 package io.cosmostation.suikotlin.model
 
 sealed class Network(val name: String, val rpcUrl: String, val faucetUrl: String) {
+    class Mainnet : Network("Mainnet", "https://sui-mainnet-us-1.cosmostation.io", "")
+
     class Devnet : Network("Devnet", "https://sui-devnet-kr-1.cosmostation.io", "https://faucet.devnet.sui.io")
 
     class Testnet : Network("Testnet", "https://sui-testnet-kr-1.cosmostation.io", "https://faucet.testnet.sui.io")