refactor: settlement transactions

[bernoullithedev]

Updated the SettlementTransaciton interface by introducing the following enhancements:

1. Added missing nested object types: Customer, SubAccount, and Authorization
2. Used utility types (Omit) to tailor the nested types and exclude properties not returned in the settlement transaction response

[tekpriest]

It’s better to explicitly pick the fields we want to expose rather than omitting several, as Omit can unintentionally allow fields to slip through if the SubAccount type changes in the future. Using Pick (or a dedicated response type) makes the contract clearer, more secure, and easier to maintain.