feat: Refactor PaymentGateway implementations using macros
- Introduced a new macro system for PaymentGateway implementations to reduce boilerplate code and improve maintainability.
- Created `impl_payment_gateway_todo!` macro for flows pending UCS GRPC endpoints, replacing manual TODO implementations in `authorize.rs`.
- Implemented `define_ucs_executor!` macro to generate UCS executor structs for GRPC endpoint integration.
- Updated `authorize.rs` to utilize the new macros, significantly reducing lines of code and improving clarity.
- Added `macros.rs` to define the new macros and organized the module structure in `mod.rs`.
- Documented the usage and benefits of the new macro system in `MACRO_REFACTORING.md`.
