Added USDC for arbOne and ArbSepolia

[EmreDincoglu]

Description

Added default stablecoin for Arbitrum One and Arbitrum Sepolia across all three SDKS via the guide in DEFAULT_ASSET.md
Except sent the TS changes to the new location shown below

Field	Value
Network	eip155:42161 (Arbitrum One)
Asset	0xaf88d065e77c8cC2239327C5EDb3A432268e5831
EIP-712 name	USDC Coin
EIP-712 version	2
Decimals	6

Field	Value
Network	eip155:421614 (Arbitrum Sepolia)
Asset	0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d
EIP-712 name	USDC Coin
EIP-712 version	2
Decimals	6

Files changed

• TypeScript: typescript/packages/mechanisms/evm/src/shared/defaultAssets.ts
• Python: python/x402/mechanisms/evm/constants.py
• Go: go/mechanisms/evm/constants.go
• Changesets: TS .changeset, Go .changes/unreleased yaml, Python changelog.d feature.md

Tests

Verified EIP:712 parameters by re-hashing other USDC entries and comparing it to the DOMAIN_SEPARATOR on both chains to make sure its the same on Arb One and Arb Sepolia

Verified USDC contract address by looking at both ArbiScan and USDC contracts docs page

Ran the tests said in Contributions page, everything passed, the python SDK did skip 32 but none failed

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

[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 2 if repo is sensitive 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

[vercel]

@EmreDincoglu is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[phdargen]

Thanks @EmreDincoglu 🚀