feat: add guruTestnet chain

[Kharabet]

This PR introduces the Guru Network Testnet to the project, enhancing the chain definitions with its details and enabling its export for use in other parts of the application.

Before creating the pull request, please make sure you do the following:

• Added guruTestnet export in src/chains/index.ts.
• Created guruTestnet definition in src/chains/definitions/guruTestnet.ts with:
  • ID: 261
  • Native currency: tGURU (18 decimals)
  • RPC URLs for HTTP
  • Multicall3 contract details
  • Block explorer information (Guruscan)
  • Marked as a testnet.

---

PR-Codex overview

This PR introduces the guruTestnet chain to the project, allowing integration with the Guru Network Testnet.

Detailed summary

• Added a new chain definition for guruTestnet in src/chains/definitions/guruTestnet.ts.
• Defined properties for guruTestnet including id, name, nativeCurrency, rpcUrls, and blockExplorers.
• Exported guruTestnet from src/chains/index.ts.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 269035b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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viem	Patch

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[jxom]

Removed multicall contract as it is unverified. Please open another PR with the verified contract.