fix: refactor refund core

[NishantJoshi00]

Description

The division of the refund core into modular functions isn't in place, whilst the functionalities that are being called are used in multiple places for different use cases. The refactoring of the refund core is necessary.

Changes

• In the refactoring the core execution logic of the refund must be separated from the schedule_refund_execution function
• Function for executing instant refund and scheduled refund must be separated