Add THAT Mainnet

[qi-0826]

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PR-Codex overview

This PR introduces support for the THAT Mainnet chain within the codebase by adding its definition and exporting it for use.

Detailed summary

• Added a new entry for that in src/chains/index.ts.
• Created that.ts in src/chains/definitions/ with the following details:
  • id: 8428
  • name: 'THAT Mainnet'
  • nativeCurrency: 'THAT', symbol 'THAT', decimals 18
  • rpcUrls: includes mainnet URL
  • blockExplorers: includes Blockscout URL
  • Set testnet to false

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🦋 Changeset detected

Latest commit: 837448d

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

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