feat: add blockTime for Arbitrum chain (#3814)

* Add arbitrum block time

* Create famous-pans-act.md

---------

Co-authored-by: jxom <[email protected]>

Author: b-tarczynski

.changeset/famous-pans-act.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Add `blockTime` to Arbitrum chains.

src/chains/definitions/arbitrum.ts

@@ -4,6 +4,7 @@ export const arbitrum = /*#__PURE__*/ defineChain({
   id: 42_161,
   name: 'Arbitrum One',
   nativeCurrency: { name: 'Ether', symbol: 'ETH', decimals: 18 },
+  blockTime: 250,
   rpcUrls: {
     default: {
       http: ['https://arb1.arbitrum.io/rpc'],

src/chains/definitions/arbitrumSepolia.ts

@@ -3,6 +3,7 @@ import { defineChain } from '../../utils/chain/defineChain.js'
 export const arbitrumSepolia = /*#__PURE__*/ defineChain({
   id: 421_614,
   name: 'Arbitrum Sepolia',
+  blockTime: 250,
   nativeCurrency: {
     name: 'Arbitrum Sepolia Ether',
     symbol: 'ETH',