Add Forma mainnet and Sketchpad testnet chains

[mycodecrafting]

PR adds Forma's mainnet and testnet

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PR-Codex overview

This PR adds Forma mainnet and Sketchpad testnet chains to the project.

Detailed summary

• Added forma chain definition with RPC URLs and block explorer.
• Added sketchpad chain definition with RPC URLs and block explorer.
• Updated src/chains/index.ts to export forma and sketchpad definitions.

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🦋 Changeset detected

Latest commit: 37fb94d8ef0fde565dbfeef4e84399c328f60490

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

This PR includes changesets to release 1 package

| Name | Type | | ---- | ----- | | viem | Patch |

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