Add createAssetPayment function

[MissBlue00]

Task

Add a createAssetPayment function to send payments in non-XLM Stellar assets.

Details

• Function signature: createAssetPayment(params: AssetPaymentParams): Promise<PaymentResult>
• Support custom Stellar assets (issued assets)
• Handle trustline verification
• Include asset code, issuer, and amount
• Add AssetPaymentParams and PaymentResult interfaces

Test

Run pnpm --filter @stellar-pay/payments-engine build to verify no TypeScript errors.

[BigNathan1]

@BigNathan1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I can resolve this issue accurately and precise within the hour. Please assign it to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @BigNathan1 to this issue.