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/services/inventory/inventory.service.js

@@ -12,9 +12,9 @@ const availabilityStatus = ({ on_hand, reserved, low_stock_threshold }) => {
   return available <= 0 ? "OUT_OF_STOCK" : available <= Number(low_stock_threshold) ? "LOW_STOCK" : "IN_STOCK";
 };
 
-async function adjustStock({ eventId, warehouseId, variantId, quantityDelta, reason, actorUserId, requestId }) {
+async function adjustStock({ eventId, warehouseId, variantId, quantityDelta, reason, actorUserId, requestId, transaction: externalTransaction }) {
   if (!eventId || !Number.isInteger(quantityDelta) || quantityDelta === 0) throw fault("A non-zero integer adjustment and eventId are required", "INVALID_ADJUSTMENT");
-  return db.sequelize.transaction(async transaction => {
+  const execute = async transaction => {
     const prior = await db.InventoryTransaction.findOne({ where: { event_id: eventId }, transaction, lock: transaction.LOCK.UPDATE });
     if (prior) return { idempotent: true, transaction: prior };
     let balance = await lockBalance(warehouseId, variantId, transaction);
@@ -24,7 +24,8 @@ async function adjustStock({ eventId, warehouseId, variantId, quantityDelta, rea
     await balance.update({ on_hand: next }, { transaction });
     const entry = await ledger({ event_id: eventId, warehouse_id: warehouseId, variant_id: variantId, type: "ADJUSTMENT", quantity_delta: quantityDelta, reason, actor_user_id: actorUserId, request_id: requestId }, transaction);
     return { balance, transaction: entry, idempotent: false };
-  });
+  };
+  return externalTransaction ? execute(externalTransaction) : db.sequelize.transaction(execute);
 }
 
 async function selectWarehouse(variantId, quantity, transaction) {