Add createSep24Withdrawal flow function

[MissBlue00]

Task

Add a createSep24Withdrawal function to implement SEP-24 withdrawal flow for off-ramping.

Details

• Function signature: createSep24Withdrawal(params: WithdrawalParams): Promise<WithdrawalResponse>
• Implement Stellar Ecosystem Proposal 24 withdrawal flow
• Handle anchor account validation
• Track withdrawal status through completion
• Add WithdrawalParams and WithdrawalResponse interfaces
• Integration point: anchor-service package

Test

Run pnpm --filter @stellar-pay/anchor-service build to verify no TypeScript errors.

[Praizfotos]

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

HELLO PLEASE I'D LOVE TO WORK ON THIS ISSUES

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