Add payWithToken Function for ERC20 Token Payments

[spencerstock]

What changed? Why?

Added payWithToken function to enable ERC20 token payments across multiple chains, extending beyond the existing USDC-only payment functionality.

Key changes:

• New payWithToken API: Supports ERC20 token transfers with customizable paymaster configuration across multiple chains (Base, Optimism, Arbitrum, Polygon, Avalanche, BSC)
• Token registry: Whitelisted support for USDC, USDT, DAI, and EURC with automatic symbol-to-address resolution
• Enhanced getPaymentStatus: Automatically extracts token transfer details from transaction logs with proper chain context
• Paymaster integration: Flexible paymaster URL configuration per chain for gasless transactions
• Telemetry: Added event tracking for payWithToken lifecycle (started, completed, error)
• Validation utilities: Base unit amount validation

How was this tested?

Test coverage for:

• payWithToken function with valid/invalid inputs
• Token registry address resolution
• Payment status checking with token transfer detection

How can reviewers manually test these changes?

1. Navigate to the pay playground testapp
2. Scroll to the "payWithToken Function" section
3. Configure token, amount, recipient, and paymaster URL
4. Execute payment and verify transaction completes
5. Check getPaymentStatus section auto-populates with transaction ID
6. Verify payment status displays token amount, symbol, and recipient

Demo/screenshots

[cb-heimdall]

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