Refactor and improve billing module

The billing module has been refined and enhanced to include deeper validation and detailing of billing plans and products. The checkout session creation process was revised to handle more complex scenarios, incorporating better parsing and validation. Additional validations were added for the plan and product schemas, improving product details extraction, and rearranging of module exports was made for better organization. The code refactor allows easier future modifications and upgrades for recurring and one-time payments with nuanced product configurations.

packages/features/accounts/package.json

@@ -15,6 +15,7 @@
     "./hooks/*": "./src/hooks/*.ts"
   },
   "devDependencies": {
+    "@kit/billing-gateway": "*",
     "@kit/eslint-config": "0.2.0",
     "@kit/prettier-config": "0.1.0",
     "@kit/shared": "*",