Add sub account SDK helper methods

[cb-jake]

Add SDK Utility methods

Changes

• Renamed accounts namespace to subaccount for consistency
• Added subaccount.create() method for creating new smart wallets
• Added subaccount.get() method for retrieving existing wallets
• Added subaccount.addOwner() method that accepts either:
  • An Ethereum address
  • A public key (as compressed hex)
• Added comprehensive test coverage for all new methods
• Updated example app to use production keys URL

Testing Instructions

1. Create a new smart wallet:

const sdk = createCoinbaseWalletSDK({...});
await sdk.subaccount.create("0x123..."); // signer address

2. Add an owner by address:

await sdk.subaccount.addOwner({
  address: "0xabc..." 
});

3. Add an owner by public key:

await sdk.subaccount.addOwner({
  publicKey: "0x7da44d..." // compressed public key
});

4. Verify the new owner can sign transactions for the wallet

Test Coverage

• Added tests for error cases (missing signer, missing account)
• Added tests for both address and public key flows
• Added integration test in example app

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[fan-zhang-sv]

ty!