Etherlink shadownet chain (#8611)

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[SDK] Feature: Add Etherlink Shadownet Testnet chain

## Notes for the reviewer

Adds the Etherlink Shadownet testnet chain (ID 127823) to the predefined chains in the SDK. This includes its native currency (XTZ) and block explorer URL.

## How to test

- Verify the `etherlinkShadownet` chain can be imported from `thirdweb/chains`.
- Check that the chain object contains the correct `id`, `name`, `nativeCurrency`, and `blockExplorers` properties.
- Run `pnpm build` and `pnpm lint` to ensure no new issues are introduced.

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[Slack Thread](https://thirdwebdev.slack.com/archives/C09DS2CKGP2/p1767789368607579?thread_ts=1767789368.607579&cid=C09DS2CKGP2)

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## PR-Codex overview
This PR introduces the `Etherlink Shadownet` testnet chain to the project, defining its properties and adding it to the exports.

### Detailed summary
- Added a new chain definition for `etherlinkShadownet` in `etherlink-shadownet.ts`.
- Defined properties such as `id`, `name`, `nativeCurrency`, and `blockExplorers`.
- Exported `etherlinkShadownet` in `chains.ts` for use in the application.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

* **New Features**
  * Added support for Etherlink Shadownet testnet chain, enabling development and testing on this network with proper block explorer integration and native currency configuration (XTZ).

<sub>✏️ Tip: You can customize this high-level summary in your review settings.</sub>

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.changeset/etherlink-shadownet-chain.md

@@ -0,0 +1,5 @@
+---
+"thirdweb": patch
+---
+
+Add Etherlink Shadownet testnet chain (chain ID 127823)

packages/thirdweb/src/chains/chain-definitions/etherlink-shadownet.ts

@@ -0,0 +1,21 @@
+import { defineChain } from "../utils.js";
+
+/**
+ * @chain
+ */
+export const etherlinkShadownet = /* @__PURE__ */ defineChain({
+  blockExplorers: [
+    {
+      name: "Etherlink Shadownet Explorer",
+      url: "https://shadownet.explorer.etherlink.com/",
+    },
+  ],
+  id: 127823,
+  name: "Etherlink Shadownet",
+  nativeCurrency: {
+    decimals: 18,
+    name: "Etherlink",
+    symbol: "XTZ",
+  },
+  testnet: true,
+});

packages/thirdweb/src/exports/chains.ts

@@ -32,6 +32,7 @@ export { degen } from "../chains/chain-definitions/degen.js";
 // mainnet = alias for ethereum
 export { ethereum, mainnet } from "../chains/chain-definitions/ethereum.js";
 export { etherlink } from "../chains/chain-definitions/etherlink.js";
+export { etherlinkShadownet } from "../chains/chain-definitions/etherlink-shadownet.js";
 export { etherlinkTestnet } from "../chains/chain-definitions/etherlink-testnet.js";
 export { fantom } from "../chains/chain-definitions/fantom.js";
 export { fantomTestnet } from "../chains/chain-definitions/fantom-testnet.js";