feat: Implement return and refund functionality in commerce module

- Added return request handling in return.controller.js
- Implemented webhook handling for PayHere payments in webhook.controller.js
- Created models for coupon redemptions, invoices, orders, order items, payments, payment attempts, payment webhook events, refunds, return items, and return requests.
- Developed services for order management, payment processing, refunds, and returns.
- Introduced validation schemas for payment and return requests.
- Created migration scripts for new database tables related to orders, payments, refunds, and returns.
- Added unit tests for order state transitions and PayHere provider functionality.

app/models/commerce/returnRequest.model.js

@@ -0,0 +1 @@
+module.exports=(s,D)=>s.define("ReturnRequest",{id:{type:D.STRING,primaryKey:true},return_number:{type:D.STRING(80),allowNull:false,unique:true},order_id:{type:D.STRING,allowNull:false},user_id:{type:D.STRING,allowNull:false},status:{type:D.ENUM("REQUESTED","APPROVED","REJECTED","AWAITING_RETURN","IN_TRANSIT","RECEIVED","INSPECTING","COMPLETED","CANCELLED"),allowNull:false},reason_code:{type:D.STRING(80),allowNull:false},reason_text:D.STRING(500),requested_at:{type:D.DATE,allowNull:false},approved_at:D.DATE,received_at:D.DATE,completed_at:D.DATE},{tableName:"return_requests",timestamps:true});