Add Robinhood Chain Testnet (46630)

[a-thomas-22]

Adds metadata for Robinhood Chain Testnet, an Arbitrum L2 testnet chain settling on Ethereum Sepolia.

• chainId: 46630
• shortName: rh-testnet
• Public RPC: https://rpc.testnet.chain.robinhood.com/rpc
• Explorer: https://explorer.testnet.chain.robinhood.com (Blockscout, EIP-3091 compatible)
• Parent: Ethereum Sepolia (eip155-11155111)
• Native currency: ETH

Verified:

• eth_chainId -> 0xb626 (46630)
• Blockscout explorer responds 200 on /block/{n} and /tx/{hash} (EIP-3091 routes)
• No existing chainId 46630 or shortName rh-testnet collision in _data/chains/
• File validates against tools/schema/chainSchema.json (required fields, shortName pattern, types)

[github-actions]

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