add Flow's previewnet evm network

.changeset/gentle-jokes-rule.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Add Flow previewnet evm network

src/chains/definitions/flowPreviewnet.ts

@@ -0,0 +1,23 @@
+import { defineChain } from '../../utils/chain/defineChain.js'
+
+export const flowPreviewnet = /*#__PURE__*/ defineChain({
+  id: 646,
+  name: 'Flow Previewnet',
+  network: 'previewnet',
+  nativeCurrency: {
+    decimals: 18,
+    name: 'Flow',
+    symbol: 'FLOW',
+  },
+  rpcUrls: {
+    default: {
+        http: ['https://previewnet.evm.nodes.onflow.org']
+    },
+  },
+  blockExplorers: {
+    default: {
+      name: 'Previewnet Explorer',
+      url: 'https://previewnet.flowdiver.io',
+    },
+  },
+})

src/chains/index.ts

@@ -72,6 +72,7 @@ export { filecoinCalibration } from './definitions/filecoinCalibration.js'
 export { filecoinHyperspace } from './definitions/filecoinHyperspace.js'
 export { flare } from './definitions/flare.js'
 export { flareTestnet } from './definitions/flareTestnet.js'
+export { flowPreviewnet } from './definitions/flowPreviewnet.js'
 /** @deprecated Use `anvil` instead. */
 export { foundry } from './definitions/foundry.js'
 export { fraxtal } from './definitions/fraxtal.js'