chore: complete the payment service

src/common/transformers/decimal.transformer.ts

@@ -0,0 +1,16 @@
+// eslint-disable-next-line import/no-named-as-default
+import Decimal from "decimal.js";
+
+export class DecimalTransformer {
+  to(value: Decimal | string | number): string {
+    return new Decimal(value).toString();
+  }
+
+  from(value: string): number {
+    return new Decimal(value).toNumber();
+  }
+}
+
+export function decimal(value: Decimal | number | string): number {
+  return new Decimal(value).toNumber();
+}