feat: add settlement_type to SalesInvoice model and related DTOs

- Added settlement_type field to SalesInvoice model with ENUM values (CASH, CREDIT, MIXED).
- Updated SalesInvoice aggregate types, input types, and where filters to include settlement_type.
- Modified StatisticsService to calculate credit amounts based on settlement_type.
- Enhanced TspProviderOriginalSendPayloadDto to include settlement_type.
- Updated NamaProvider DTOs and utility functions to handle new settlement_type logic.
- Created migration to add settlement_type column to sales_invoices table and backfill existing records.

prisma/migrations/20260524112633_add_settlement_type/migration.sql

@@ -0,0 +1,10 @@
+-- Add as nullable first to support existing rows, backfill, then enforce NOT NULL
+ALTER TABLE `sales_invoices`
+  ADD COLUMN `settlement_type` ENUM('CASH', 'CREDIT', 'MIXED') NULL;
+
+UPDATE `sales_invoices`
+SET `settlement_type` = 'CASH'
+WHERE `settlement_type` IS NULL;
+
+ALTER TABLE `sales_invoices`
+  MODIFY `settlement_type` ENUM('CASH', 'CREDIT', 'MIXED') NOT NULL;