networkDesign: change DB data type of fitness from numeric to double

The `decimal` knex data type converts by default to a `numeric(8,2)` in
postgres, effectively making maxing the value to 6 digits with 2
decimals. We use `double` instead to support any floating point value for
the fitness score, as it can be quite high for large simulations, for
example, with many thousands OD trip pairs, the value can be in the
millions or tens of millions. This converts to `double precision` in postgres.

Author: tahini

packages/transition-backend/src/models/db/migrations/20260214104900_updateNetworkDesignFitnessType.ts

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2026, Polytechnique Montreal and contributors
+ *
+ * This file is licensed under the MIT License.
+ * License text available at https://opensource.org/licenses/MIT
+ */
+import { Knex } from 'knex';
+
+const tableName = 'tr_jobs_network_design_results';
+const simulationMethodTableName = 'tr_jobs_network_design_simulation_results';
+
+/**
+ * Update the fitness score type from decimal to float to avoid large
+ * fitnesses scores causing database errors.
+ * @param knex
+ * @returns
+ */
+export async function up(knex: Knex): Promise<unknown> {
+    await knex.schema.alterTable(simulationMethodTableName, (table: Knex.TableBuilder) => {
+        table.double('fitness_score').notNullable().alter();
+    });
+    return knex.schema.alterTable(tableName, (table: Knex.TableBuilder) => {
+        table.double('total_fitness').notNullable().alter();
+    });
+}
+
+export async function down(knex: Knex): Promise<unknown> {
+    await knex.schema.alterTable(simulationMethodTableName, (table: Knex.TableBuilder) => {
+        table.decimal('fitness_score').notNullable().alter();
+    });
+    return knex.schema.alterTable(tableName, (table: Knex.TableBuilder) => {
+        table.decimal('total_fitness').notNullable().alter();
+    });
+}